Docker images are pushed on merge and release

I wasn't planning to change the filestructure so much (splitting .gitlab-ci into multiple files), but the previous setup was giving me issues. Most defaults were python related and not applicable to the docker stuff. This way there is a clearer separation.

Docker images can be found here: https://gitlab.com/OpenLabAutomation/lab-automation-packages/laborchestrator/container_registry/9084196