Fix sphinx warnings and show inheritance in API docs

[JeanChristopheMorinPerso]

Fixes #1565 Fixes #1574

This PR removes a significant number of Sphinx warnings and errors than were coming from autodoc.

It also adds inheritance information automagically.

There is 2 errors left and 13 warnings left.

docs/source/commands/rez-config.rst:28: ERROR: Unknown target name: "rez".
docs/source/package_commands.rst:593: WARNING: duplicate object description of optionvars, other instance in configuring_rez, use :no-index: for one of them
docs/source/package_definition.rst:924: WARNING: duplicate object description of version, other instance in package_commands, use :no-index: for one of them
src/rez/vendor/version/version.py:docstring of rez.vendor.version.version.AlphanumericVersionToken:12: ERROR: Unexpected indentation.
src/rez/vendor/version/version.py:docstring of rez.vendor.version.version.VersionRange:28: WARNING: Definition list ends without a blank line; unexpected unindent.
src/rez/build_process.py:docstring of rez.build_process.BuildProcess.__init__:1: WARNING: py:class reference target not found: DEPRECATED
src/rez/build_process.py:docstring of rez.build_process.BuildProcess.__init__:1: WARNING: py:class reference target not found: DEPRECATED
src/rez/build_process.py:docstring of rez.build_process.BuildProcess.__init__:1: WARNING: py:class reference target not found: DEPRECATED
src/rez/build_process.py:docstring of rez.build_process.BuildProcess.__init__:1: WARNING: py:class reference target not found: DEPRECATED
src/rez/rex.py:docstring of rez.rex.EnvironmentDict.keys:1: WARNING: py:class reference target not found: a set-like object providing a view on D's keys
src/rez/utils/pip.py:docstring of rez.utils.pip.pip_to_rez_version:1: WARNING: py:exc reference target not found: InvalidVersion
src/rez/utils/pip.py:docstring of rez.utils.pip.convert_distlib_to_setuptools:1: WARNING: py:class reference target not found: installed_dist
src/rez/vendor/version/test.py:docstring of rez.vendor.version.test.TestVersionSchema:1: WARNING: py:class reference target not found: unittest.case.TestCase
src/rez/vendor/version/version.py:docstring of rez.vendor.version.version.VersionRange.iter_intersect_test:1: WARNING: py:class reference target not found: callable
src/rez/vendor/version/version.py:docstring of rez.vendor.version.version.VersionRange.visit_versions:1: WARNING: py:class reference target not found: callable

[brycegbrazen]

Thanks for the new type hinting additions and cleanup! Much appreciated 💯 LGTM

[JeanChristopheMorinPerso]

Great. There could have been way more type hints, but I gave up pretty quickly. It's a boring task and I have to say that my time right now is better spent in other areas.