CI: Cloud Build to validate and test Terraform scripts

[markmandel]

We'll need a Google Cloud Project to host this on, so that when PR's come into the project, we have at least some kind of CI testing for the GitHub repository.

I would do this in a few steps:

• Create a blank cloudbuild.yaml in the root of the project (and get this PR merged)
• Create a Google Cloud project and connect to it with the GitHub App
• Expand the CI to include the basic terraform tests, like init, validate, fmt, etc with a secondary PR.

Possibly relevent: https://www.hashicorp.com/blog/testing-hashicorp-terraform for future efforts, but don't have to be included in this ticket.

[markmandel]

Discussion point: if we don't want to go full Google Cloud project and the responsibilities therein - we could also use GitHub actions to do the same.