Build docker artifact

Building the containers and pushing the built artifacts into the gitlab docker registry https://git.gfz-potsdam.de/dynamicexposure/server-components/containers/docker-obm-database/container_registry. This will allow to test e.g. the migrations in database-obmbuildings. The image can be pulled and run straight from the gitlab registry:

docker run git.gfz-potsdam.de:5000/dynamicexposure/server-components/containers/docker-obm-database:feature-docker-build-ci

I scheduled a weekly job to rebuild the image on master to make sure it keeps up to date.

Useful also for this MR: https://git.gfz-potsdam.de/dynamicexposure/openbuildingmap/database-obmbuildings/-/merge_requests/6

\rfc @fd \fyi @ds @prehn