towards k8s

This MR combines several edits to make the app and built containers ready for kubernetes. mainly:

• allow reading secrets from file instead of (in container systems externally immutable) env vars
• adjustments to the GitLab CI pipeline
• new: build script for local k8s (k3d based) dev environment

Also it fixes a fatal issue with the search interface (missing var in commons was moved to function).

Following this MR a corresponding MR in the helm chart project will be set up.