WIP: Feature: Rapid CDN

Design:

• provide user friendly approach
  • fast frontend connection parameter provision
  • asynchronous frontend creation with informative page
  • good defaults:
    • https-only
    • full caching
    • backend checks
  • websocket support
• have compatibility layer for custom-personal from caddy-frontend
  • full for scenarios like massive automatic hosting, forever due to return parameters
  • encourage migration for parameters like type
• haproxy only (https://lab.nexedi.com/nexedi/slapos/merge_requests/830)
• cluster based CA (https://lab.nexedi.com/nexedi/slapos/merge_requests/843)