Add a script for migrating the database
Part of https://gitlab.com/charts/helm.gitlab.io/issues/97
Adds a script for migrating the db from a rails container. (Based on what we do in omnibus)
Add some wait for functionality that allows the rails container to wait for the database connection. (Allowing us to finally just use docker-compose up
in this repo, and will be used in initContainers in the charts)