Properly handle multiple static-sites with the same domain (and multiple proxied-services with the same domain)

Currently, with two such definitions one will be silently dropped. This should instead be an error unless the two are compatible (e.g. two proxied-services with a different prefix)

Trace where static-sites and proxied-services definitions are parsed and validated, then inspect how duplicate domains are currently resolved or dropped. Done means incompatible duplicate domains produce an error, while compatible proxied-services with different prefixes remain accepted.

Written by the indexing model from the issue text.