Use healthy rather than healthz for healthcheck endpoint.
This ensures that the healthcheck endpoint can be reached when deployed to cloud run - see https://gitlab.developers.cam.ac.uk/uis/devops/iam/photo-api/-/merge_requests/7#note_212193
This ensures that the healthcheck endpoint can be reached when deployed to cloud run - see https://gitlab.developers.cam.ac.uk/uis/devops/iam/photo-api/-/merge_requests/7#note_212193