Make docs useful again (#519)

## Changes
The last refactor to docs introduced dataclasses and enum documentation
but regressed on examples and ease of use/navigability by introducing
extremely long pages with many different APIs and classes documented.
This has led to some confusion for users of the SDK who are simply
trying to explore/understand what functionality is supported.

This PR undoes that refactor while preserving the dataclass and enum
documentation, and it even improves on it somewhat, reducing a
substantial amount of visual noise from dataclass constructor signatures
and making enum values easier to read and understand.

Link to preview:
https://databricks-sdk-py--519.org.readthedocs.build/en/519/

## Tests
<!-- 
How is this tested? Please see the checklist below and also describe any
other relevant tests
-->

- [ ] `make test` run locally
- [ ] `make fmt` applied
- [ ] relevant integration tests applied

docs/account/billing/billable_usage.rst

@@ -0,0 +1,44 @@
+``a.billable_usage``: Billable usage download
+=============================================
+.. currentmodule:: databricks.sdk.service.billing
+
+.. py:class:: BillableUsageAPI
+
+    This API allows you to download billable usage logs for the specified account and date range. This feature
+    works with all account types.
+
+    .. py:method:: download(start_month: str, end_month: str [, personal_data: Optional[bool]]) -> DownloadResponse
+
+
+        Usage:
+
+        .. code-block::
+
+            from databricks.sdk import AccountClient
+            
+            a = AccountClient()
+            
+            resp = a.billable_usage.download(start_month="2023-01", end_month="2023-02")
+
+        Return billable usage logs.
+
+        Returns billable usage logs in CSV format for the specified account and date range. For the data
+        schema, see [CSV file schema]. Note that this method might take multiple minutes to complete.
+
+        **Warning**: Depending on the queried date range, the number of workspaces in the account, the size of
+        the response and the internet speed of the caller, this API may hit a timeout after a few minutes. If
+        you experience this, try to mitigate by calling the API with narrower date ranges.
+
+        [CSV file schema]: https://docs.databricks.com/administration-guide/account-settings/usage-analysis.html#schema
+
+        :param start_month: str
+          Format: `YYYY-MM`. First month to return billable usage logs for. This field is required.
+        :param end_month: str
+          Format: `YYYY-MM`. Last month to return billable usage logs for. This field is required.
+        :param personal_data: bool (optional)
+          Specify whether to include personally identifiable information in the billable usage logs, for
+          example the email addresses of cluster creators. Handle this information with care. Defaults to
+          false.
+
+        :returns: :class:`DownloadResponse`
+

docs/account/billing/budgets.rst

@@ -0,0 +1,162 @@
+``a.budgets``: Budgets
+======================
+.. currentmodule:: databricks.sdk.service.billing
+
+.. py:class:: BudgetsAPI
+
+    These APIs manage budget configuration including notifications for exceeding a budget for a period. They
+    can also retrieve the status of each budget.
+
+    .. py:method:: create(budget: Budget) -> WrappedBudgetWithStatus
+
+
+        Usage:
+
+        .. code-block::
+
+            import time
+            
+            from databricks.sdk import AccountClient
+            from databricks.sdk.service import billing
+            
+            a = AccountClient()
+            
+            created = a.budgets.create(budget=billing.Budget(
+                name=f'sdk-{time.time_ns()}',
+                filter="tag.tagName = 'all'",
+                period="1 month",
+                start_date="2022-01-01",
+                target_amount="100",
+                alerts=[billing.BudgetAlert(email_notifications=["admin@example.com"], min_percentage=50)]))
+            
+            # cleanup
+            a.budgets.delete(budget_id=created.budget.budget_id)
+
+        Create a new budget.
+
+        Creates a new budget in the specified account.
+
+        :param budget: :class:`Budget`
+          Budget configuration to be created.
+
+        :returns: :class:`WrappedBudgetWithStatus`
+
+
+    .. py:method:: delete(budget_id: str)
+
+        Delete budget.
+
+        Deletes the budget specified by its UUID.
+
+        :param budget_id: str
+          Budget ID
+
+
+
+
+    .. py:method:: get(budget_id: str) -> WrappedBudgetWithStatus
+
+
+        Usage:
+
+        .. code-block::
+
+            import time
+            
+            from databricks.sdk import AccountClient
+            from databricks.sdk.service import billing
+            
+            a = AccountClient()
+            
+            created = a.budgets.create(budget=billing.Budget(
+                name=f'sdk-{time.time_ns()}',
+                filter="tag.tagName = 'all'",
+                period="1 month",
+                start_date="2022-01-01",
+                target_amount="100",
+                alerts=[billing.BudgetAlert(email_notifications=["admin@example.com"], min_percentage=50)]))
+            
+            by_id = a.budgets.get(budget_id=created.budget.budget_id)
+            
+            # cleanup
+            a.budgets.delete(budget_id=created.budget.budget_id)
+
+        Get budget and its status.
+
+        Gets the budget specified by its UUID, including noncumulative status for each day that the budget is
+        configured to include.
+
+        :param budget_id: str
+          Budget ID
+
+        :returns: :class:`WrappedBudgetWithStatus`
+
+
+    .. py:method:: list() -> Iterator[BudgetWithStatus]
+
+
+        Usage:
+
+        .. code-block::
+
+            from databricks.sdk import AccountClient
+            
+            a = AccountClient()
+            
+            all = a.budgets.list()
+
+        Get all budgets.
+
+        Gets all budgets associated with this account, including noncumulative status for each day that the
+        budget is configured to include.
+
+        :returns: Iterator over :class:`BudgetWithStatus`
+
+
+    .. py:method:: update(budget_id: str, budget: Budget)
+
+
+        Usage:
+
+        .. code-block::
+
+            import time
+            
+            from databricks.sdk import AccountClient
+            from databricks.sdk.service import billing
+            
+            a = AccountClient()
+            
+            created = a.budgets.create(budget=billing.Budget(
+                name=f'sdk-{time.time_ns()}',
+                filter="tag.tagName = 'all'",
+                period="1 month",
+                start_date="2022-01-01",
+                target_amount="100",
+                alerts=[billing.BudgetAlert(email_notifications=["admin@example.com"], min_percentage=50)]))
+            
+            a.budgets.update(budget_id=created.budget.budget_id,
+                             budget=billing.Budget(name=f'sdk-{time.time_ns()}',
+                                                   filter="tag.tagName = 'all'",
+                                                   period="1 month",
+                                                   start_date="2022-01-01",
+                                                   target_amount="100",
+                                                   alerts=[
+                                                       billing.BudgetAlert(email_notifications=["admin@example.com"],
+                                                                           min_percentage=70)
+                                                   ]))
+            
+            # cleanup
+            a.budgets.delete(budget_id=created.budget.budget_id)
+
+        Modify budget.
+
+        Modifies a budget in this account. Budget properties are completely overwritten.
+
+        :param budget_id: str
+          Budget ID
+        :param budget: :class:`Budget`
+          Budget configuration to be created.
+
+
+

docs/account/billing/index.rst

@@ -0,0 +1,12 @@
+
+Billing
+=======
+
+Configure different aspects of Databricks billing and usage.
+
+.. toctree::
+   :maxdepth: 1
+
+   billable_usage
+   budgets
+   log_delivery