Auto GUID enhancements

> You must enable auto GUID generation for your PRs by following the instructions here https://github.com/google/digitalbuildings/blob/master/CONTRIBUTING.md#enabling-auto-guid-generation-for-prs
>
> Auto-generation does not work for your first PR (you submitted your first PR last week) -- if the GUIDs aren't automatically added, please add manually by generating an UUID4 (https://www.uuidgenerator.net/) and inserting into your branch.

Looks like the GUIDs are only generated on **push**es to a branch called master. Is there a reason that the logic doesn't allow GUID generation on **pull-request**s to your master branch? I don't mind producing another PR to expand this to improve outside engagement, but I'm weary of stepping on toes (or there could be a darn good reason not to that I'm unfamiliar with).

_Originally posted by @ohshazbot in https://github.com/google/digitalbuildings/issues/1254#issuecomment-1908395234_

Good questions -- we will need to dig into the original technical design documents before proceeding. Opening as issue to track.

Start with the auto GUID generation instructions in CONTRIBUTING.md and trace the automation that runs for pushes to the master branch. Review the original technical design documents referenced in the issue before deciding how pull requests should be handled. Done means the intended GUID generation behavior for pull requests is documented and implemented without breaking the existing push workflow.

Written by the indexing model from the issue text.