Many-to-many external domain/site association

[runleveldev]

Currently, each external domain belongs to exactly one Site. We want each external domain to be available to all sites. For each domain, a default site should be selected (optional). For each site that has access to an external domain which is not its default, an external IP address(es) should be configured. When an HTTP service is created for an external domain which is not a default of the current site, the Cloudflare API credentials used for ACME cert provisioning should be used to update the Cloudflare DNS zone with the service’s external hostname pointing to the external IP(s) of that site.