Manage the cloudbuild bucket

[akkornel]

The first time someone (with appropriate permissions) does a manual run of Cloud Build from the gcloud CLI, the CLI creates a new bucket. This happens because CLI-based builds work by uploading a .tgz file with the source.

The bucket name is [PROJECT_ID]_cloudbuild, the prefix for uploads is source, and files are named with something that looks like a timestamp plus a hash, with a .tgz extension. It doesn't look like there are any special permissions on the bucket; Cloud Build has access to the bucket through the "Cloud Build Service Account" role.

This bucket should be managed in Terraform. That'll let us do a few things:

• Auto-delete files after 18 months (365.25 * 1.5 days, which we'll round to 548 days).

• Move to Coldline after 32 days.

• Set write permissions to store some build artifacts (like package lists).

And it also lets me keep track of the bucket, in case we want to do anything else.