feat: add progress field to UpdateDatabaseDdlMetadata

[parthea]

This PR includes the latest generated client from googleapis-gen. I also modified the owlbot.py script to properly copy multiple versions from googleapis-gen here.

This PR also includes the following features and fixes:

feat: move import of CommitResponse
fix: add async client to %name_%version/init.py
chore: add autogenerated snippets
chore: remove auth, policy, and options from the reserved names list
feat: support self-signed JWT flow for service accounts
chore: enable GAPIC metadata generation
chore: sort subpackages in %namespace/%name/init.py

[parthea]

The build has the following error: ImportError: cannot import name 'CommitResponse' . I'm looking into it.

==================================== ERRORS ====================================
_________________ ERROR collecting tests/system/test_system.py _________________
ImportError while importing test module '/home/runner/work/python-spanner/python-spanner/tests/system/test_system.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/opt/hostedtoolcache/Python/3.8.10/x64/lib/python3.8/importlib/__init__.py:127: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
tests/system/test_system.py:33: in <module>
    from google.cloud.spanner_v1 import param_types
google/cloud/spanner_v1/__init__.py:37: in <module>
    from .types.spanner import CommitResponse
E   ImportError: cannot import name 'CommitResponse' from 'google.cloud.spanner_v1.types.spanner' (/home/runner/work/python-spanner/python-spanner/google/cloud/spanner_v1/types/spanner.py)
______________ ERROR collecting tests/system/test_system_dbapi.py ______________
ImportError while importing test module '/home/runner/work/python-spanner/python-spanner/tests/system/test_system_dbapi.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
/opt/hostedtoolcache/Python/3.8.10/x64/lib/python3.8/importlib/__init__.py:127: in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
tests/system/test_system_dbapi.py:23: in <module>
    from google.cloud.spanner_v1 import BurstyPool
google/cloud/spanner_v1/__init__.py:37: in <module>
    from .types.spanner import CommitResponse
E   ImportError: cannot import name 'CommitResponse' from 'google.cloud.spanner_v1.types.spanner' (/home/runner/work/python-spanner/python-spanner/google/cloud/spanner_v1/types/spanner.py)

[parthea]

There is an issue with the docs. I was able to resolve the issue by removing the headings in this docstring .

sphinx.errors.SphinxWarning: /usr/local/google/home/partheniou/git/python-spanner/google/cloud/spanner_v1/types/transaction.py:docstring of google.cloud.spanner_v1.types.transaction.TransactionOptions:4:Unexpected section title.

I'll add a workaround in owlbot.py . I've suggested an update to the source proto to remove the headings based on AIP-192. Googlers see cl/377290854

Headings and tables must not be used, as these cause problems for several tools, and are unsuitable for client library reference documentation.

[parthea]

I'm going to switch this back to draft. It should be ready for review tomorrow.