tests/functional: Add a pylintrc file

Add a pylintrc file that can be used for checking the python code of
the functional tests. For the beginning, we use some rather lax settings.
We still can refine them later if we think that there's a need for it.

Message-Id: <20251119082636.43286-2-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>