HTTPS Certs: CLoudflair DNS Challenge

[douglasg14b]

For instances that are not accessible to the internet, the default (forced) DNS resolution mode is non-functional.

Supporting other challenges which are already supported by Caddy (ie. Cloudflair DNS) will allow us to use it in a secure environment.

Similarly, docs that describe reverse proxying to Coolify and the necessary configuration would work as well. Since folks can just use their own Caddy proxy in front of it.