Deployment CI template missing migrations

Some services include a migration step as part of the deployment pipeline. See https://gitlab.developers.cam.ac.uk/uis/devops/tls-certificates/google-cloud-deploy/-/blob/dfa4de669a1e67e4d064f9fc27d022ef5c18927b/.gitlab-ci.yml#L155

When migrating TLS Certs and Shib Metadata to use the common deploy CI template we didn't implement the migration step in the template.