Add fine-grained, per-service deployment

[justb4]

Currently deployment of services/Docker containers on the testbed server VM is automatic on any commit/push to this repo.
A more fine-grained deployment is required: only the Service that has been changed needs to be redeployed.

This can be effected by having GitHub Workflow Actions that in addition to be triggered by a 'push' also filter for changes in a specific directory. e.g. if something in the Traefik dir has been changed only the Traefik Service is redeployed.

[justb4]

Done and working now, see some docu: https://github.com/Geonovum/ogc-api-testbed#selective-redeploy