Add mechanism for obtaining sockaddr for remote client in HTTP server

[gdamore]

Discussed in #1856

^{Originally posted by nanji886 August 4, 2024}
Sometimes when a request is received in the HTTP server, it needs to respond differently depending on the remote client IP. Therefore, it is very meaningful to add the function of obtaining the client's IP for the HTTP server.

Basically we should probably add an nng_sockaddr member to the http_request object. This can be useful in a variety of circumstances. It won't be useful on the client, but it would be useful to make it available to handlers.