docker frontend container

Todo

• Build image automatically using Gitlab CI
• Publish Container on the Docker Hub
• Configure renovate to add an update snippet of the compose files postgres version gets bumped by a major version

# Docs

• Update installation instructions, remove downloading of nginx configs
• Update update instructions, don't update nginx configs anymore
• Update update snippet to make sure people update their postgres version if required

Moved to !1770 (merged)