community/py3-gitlab: add missing dependency

Before this change:

    $ sudo apk add py3-gitlab
    ✂
    $ gitlab --version
    Traceback (most recent call last):
      File "/usr/bin/gitlab", line 6, in <module>
        from pkg_resources import load_entry_point
    ModuleNotFoundError: No module named 'pkg_resources'

After this change:

    $ sudo apk add py3-gitlab
    ✂
    $ gitlab --version
    2.2.0

The commands above were run inside docker-abuild using `dabuild sh`.

The change is required because `/usr/bin/gitlab` includes the line:

    from pkg_resources import load_entry_point

That means that py3-setuptools is required at runtime:

    $ python3 -c 'import pkg_resources; print(pkg_resources.__file__)'
    /usr/lib/python3.8/site-packages/pkg_resources/__init__.py
    $ apk info -q -W /usr/lib/python3.8/site-packages/pkg_resources/__init__.py
    py3-setuptools

0 files changed, 0 insertions, 0 deletions