Add service_account_name to Cloud Run V2 default template and variables

[kevingrismore]

Adds support for the serviceAccount field in the Cloud Run V2 API Job template via the service_account_name variable to improve default template parity with the V1 work pool.

Example

Screenshots

Checklist

• References any related issue by including "Closes #" or "Closes ".
  • If no issue exists and your change is not a small fix, please create an issue first.
• Includes tests or only affects documentation.
• Passes pre-commit checks.
  • Run pre-commit install && pre-commit run --all locally for formatting and linting.
• Includes screenshots of documentation updates.
  • Run mkdocs serve view documentation locally.
• Summarizes PR's changes in CHANGELOG.md

[zzstoatzz]

thanks @kevingrismore ! just one comment

[jakekaplan]

Nice! Was just looking for this 😅