server: Add Traefik support for host mode subdomains

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This is a quick follow-on to #4086, which didn’t allow the publishing to or visiting of host mode “Boxel Space” domains. With this Traefik will pass *.realm-server.environment-name.localhost requests to the environment realm server.

Currently publish requests fail like this:

[start:development          ] Error publishing realm: {
[start:development          ]   stack: 'SyntaxError: Unexpected non-whitespace character after JSON at position 4 (line 1 column 5)\n' +
[start:development          ]     '    at JSON.parse (<anonymous>)\n' +
[start:development          ]     '    at parseJSONFromBytes (node:internal/deps/undici/undici:4259:19)\n' +
[start:development          ]     '    at successSteps (node:internal/deps/undici/undici:6882:27)\n' +
[start:development          ]     '    at readAllBytes (node:internal/deps/undici/undici:5807:13)\n' +
[start:development          ]     '    at processTicksAndRejections (node:internal/process/task_queues:103:5)',
[start:development          ]   message: 'Unexpected non-whitespace character after JSON at position 4 (line 1 column 5)'
[start:development          ] }

Here it is working locally: