sg ops: add gcr image tag updates
Created by: mucles
relates to: https://github.com/sourcegraph/sourcegraph/issues/39102
sg-cli doesn't functionality to update the gcr images that we use
after adding gcr implementation, cloud SQL images are able to get upgraded without the use of renovate
Test plan
tested locally
go run ./dev/sg ops update-images -cr-username $CR_USERNAME -cr-password $CR_PASSWORD -k k8s ../deploy-sourcegraph-cloud/base