Added ci

@fd there are some issues which sqlfluff complains about. Not sure if we should use a different linter or any linter at all but I'd feel better when contributing.

Update: The ci now uses the built artifact from our docker-obm-database pulled from here: https://git.gfz-potsdam.de/dynamicexposure/server-components/containers/docker-obm-database/container_registry It's still using the produced one from the merge request. Just need to update the pulled image as soon as this is in master). It then executes all files in migrations to see if all work.

The linter complaints about a couple of issues and unparseable things. E.g. the 4 space indentation seems invalid. Should can you install the linter and give it a try. I'm not experiences enough in sql to judge if the linter is viable or not.