feat: enable hermetic code generation

[diegomarquezp]

As part of the HW library migration plan to enable multi-version support, this pull request adds three files:

• generation_config.yaml: Contains the configuration for generating this library. See its specification.
• .github/workflows/update_googleapis_committish.yaml: A workflow to update the googleapis committish defined in generation_config.yaml
• .github/workflows/hermetic_code_generation.yaml: A workflow for generate the source code changes given a change in generation_config.yaml

[conventional-commit-lint-gcf[bot]]

🤖 I detect that the PR title and the commit message differ and there's only one commit. To use the PR title for the commit history, you can use Github's automerge feature with squashing, or use automerge label. Good luck human!

-- conventional-commit-lint bot https://conventionalcommits.org/