Host default image for Gitlab on Databricks Official account on Docker Hub

[valx]

the default image for gitlab is hosted at:
https://hub.docker.com/repository/docker/databricksfieldeng/mlopsstack/general
This should be changed to be hosted on a Databricks official repo.
Once that's done, we should update the parameter input_docker_image from the current value databricksfieldeng/mlopsstacks:latest