feat(cloudflare): improve cloudflare regional hostnames implementation

[vflaux]

trafficstars

Description Improves my previous implementation of Cloudflare Regional Services (aka Regional Hostnames) by:

• adding a flag to enable Regional Services feature (disabled by default, enabled if region key is set)
• supporting deletion of regional hostnames on annotation edit: removing the annotation if the default key is empty or setting it to empty string will remove the regional hostname config
• correctly supporting differences detection with cloudflare state: periodic reconcile / restart will detect external modifications on regional hostname config
• increasing tests coverage

This implementation use a call to list regional hostnames on the zone and use them to plan changes on cloudflare.

Checklist

• [x] Unit tests updated
• [x] End user documentation updated