BREAKING CHANGE: A config file is no longer needed to run
the CLI. python-gitlab will default to https://gitlab.com
with no authentication if there is no config file provided.
python-gitlab will now also only look for configuration
in the provided PYTHON_GITLAB_CFG path, instead of merging
it with user- and system-wide config files. If the
environment variable is defined and the file cannot be
opened, python-gitlab will now explicitly fail.

It is not yet available upstream.

chore: add get() methods for GetWithoutIdMixin based classes

Add the get() methods for the GetWithoutIdMixin based classes.

Update the tests/meta/test_ensure_type_hints.py tests to check to
ensure that the get methods are defined with the correct return type.

Fix pylint error "expression-not-assigned" and remove check from the
disabled list.

And I personally think it is much more readable now and is less lines
of code.

Initial pylint check is added. A LONG list of disabled checks is also
added. In the future we should work through the list and resolve the
errors or disable them on a more granular level.

Enable 'warn_redundant_casts'for mypy and resolve one issue.

docs: only use type annotations for documentation