feat: Create/Pass commit date to commit for signing

[IchordeDionysos]

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Fixes #337 🦕

[conventional-commit-lint-gcf]

🤖 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/

[IchordeDionysos]

@googleapis/github-automation can someone review my PR, this would unblock issues in release-please to sign commits.

[IchordeDionysos]

There is some open/related discussion in this issue:
#337 (comment)

also /cc @chingor13 @SurferJeffAtGoogle

[IchordeDionysos]

@chingor13 @SurferJeffAtGoogle @bshaffer hey it would be cool to get some feedback whether this is something we can add to the package.

As it is currently the commit signing capability is broken and does not work ...