Relax requests version upper bound to <3 (#138)

## Changes
This PR allows users to use the Databricks SDK for Python with the most recent version of the requests library within the 2.x release line, enabling them to receive security patches and non-backwards-incompatible new features.

Closes #136.

## 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

setup.py

@@ -10,7 +10,7 @@
       version=version_data['__version__'],
       packages=find_packages(exclude=["tests", "*tests.*", "*tests"]),
       python_requires=">=3.7",
-      install_requires=["requests>=2.28.1,<2.29.0"],
+      install_requires=["requests>=2.28.1,<3"],
       extras_require={"dev": ["pytest", "pytest-cov", "pytest-xdist", "pytest-mock",
                               "yapf", "pycodestyle", "autoflake", "isort", "wheel"]},
       author="Serge Smertin",