Allow cloud run services requiring authentication to be monitored via an authentication proxy

Configure a Cloud Function to authenticate requests to Cloud Run instances which don't allow unauthenticated invocation.

Part of https://gitlab.developers.cam.ac.uk/uis/devops/iam/deploy-identity/-/issues/23

Tested within https://gitlab.developers.cam.ac.uk/uis/devops/iam/deploy-identity/-/merge_requests/30