Port the pre-commit jobs, CI jobs, terraform-docs and release it
configuration from the GCP CLoud Run app module.

This involved some automated and some manual fixups to files to appease
the tflint and trivy gods. In particular we needed to add a type
annotation to the `service_account` variable, change the
`service_account` output to match, rename the CHANGELOG file
and re-structure the README to be terraform-docs friendly.

Since the types of the `service_account` variable and output have
changed, mark this as a breaking feature.