feat(Homeserver): Switch API from user ID in the path to user ID as a subdomain

[Nuhvi]

Currently the AP of the homeserver is /:userid/pub/ since Pkarr is getting support for Endpoints resolution, we can do userid.<homeserver>/pub/ where the homeserver gets a direct connection and reads the HTTP host to figure out which user is being queried.

In browser, we will need to embed this subdomain inside a custom header, because we can't send a request to IP and port directly, and it is not guaranteed that the homeserver owner can run a server with a wildcard TLS certificate.

[Nuhvi]

Instead of subdomains, we are going with normal domains and use Pkarr Endpoint resolution and TLS.