[CT-1766] [DX] Review command + param help text in CLI / top-level API

[jtcohen6]

Let's give the "help" text defined below another review from a DX (Developer Experience) lens:

• https://github.com/dbt-labs/dbt-core/blob/main/core/dbt/cli/main.py
• https://github.com/dbt-labs/dbt-core/blob/main/core/dbt/cli/params.py

Anything marked TODO is especially in need, but I think all help text deserves another look-over.

This is also our opportunity to remove params / help text that are completely unused or irrelevant. For example, dbt compile --parse-only doesn't do anything, and I don't believe it ever has.

Context

This is what users will see when running dbt --help (invoked as module for now):

$ python3 -m core.dbt.cli.main --help
Usage: python -m core.dbt.cli.main [OPTIONS] COMMAND [ARGS]...

  An ELT tool for managing your SQL transformations and data models. For more
  documentation on these commands, visit: docs.getdbt.com

Options:
  --anonymous-usage-stats / --no-anonymous-usage-stats
                                  Send anonymous usage stats to dbt Labs.
  --cache-selected-only / --no-cache-selected-only
                                  Pre cache database objects relevant to
                                  selected resource only.
  -d, --debug / --no-debug        Display debug logging during dbt execution.
                                  Useful for debugging and making bug reports.

And it's also what they'll see in our auto-generated "API docs."

[jtcohen6]

@dbeatty10 Let's figure out a sprint where you have capacity to pick this up & drive this forward, between now and mid-April (RC release)

[jtcohen6]

Might be nice: using the click-option-group extension to group together related commands in the --help output (and in the codebase).

• https://click-option-group.readthedocs.io/en/stable/index.html

Not necessary for the scope for this issue, only if inspiration strikes while looking at existing params.