chore: add a configuration checker

[JoeWang1127]

In this PR:

• Add a generation configuration checker in CI.

Tested the checker by changing the configuration (commit) and the check failed:

GAPICs is None in {'api_shortname': 'accessapproval', 'name_pretty': 'Access Approval', 'product_documentation': 'https://cloud.google.com/access-approval/docs/', 'api_description': "enables controlling access to your organization's data by Google personnel.", 'release_level': 'stable', 'GAPICs': None}.
Error: Process completed with exit code 1.

[diegomarquezp]

In order to avoid specifying a custom entrypoint, it may be more convenient to have our docker image with ENTRYPOINT [ 'python', '/src/cli/entry_point.py' ] instead of ENTRYPOINT [ 'python', '/src/cli/entrypoint.py', 'generate' ]. Just a nice to have