feat: add clients for v1beta2 endpoint

[tswast]

This is 100% autogenerated code. Subsequent PRs will cover manual classes.

Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:

• Make sure to open an issue as a bug/issue before writing your code! That way we can discuss the change, evaluate designs, and agree on the general idea
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)

Fixes #<issue_number_goes_here> 🦕

TODO:

• docs build successful
• unit tests pass (need to remove test_append_rows_flattened_* tests, as there are no flattened arguments for append_rows)

[shollyman]

Always challenging filtering the real changes in these CLs vs the autogen stuff. The synth changes seem reasonable.

I don't understand the presence of both scripts/fixup_bigquery_storage_v1beta2_keywords.py and scripts/fixup_storage_v1beta2_keywords.py in this CL; is one of them spurious?

Also, I don't see these scripts referenced elsewhere; are they one off utilities or do they need to be wired into synth/nox somehow?

[shollyman]

Approving based on conversation with swast.