XXX rapid-cdn: Implement simple and working frontend support

Checkpoint: haproxy serves some backend.
2 jobs for feature/rapid-cdn in 0 seconds (queued for 1 second)
Status Job ID Name Coverage
  External
failed SlapOS.SoftwareReleases.IntegrationTest-py3-luke/feature/rapid-cdn

04:07:40

failed SlapOS.SoftwareReleases.IntegrationTest-py3-luke/feature/rapid-cdn

03:34:04