http: document how to reference http resources

[p-shahi]

Paraphrasing @MarcoPolo "HTTP semantics can run on top of any transport. So these need to be able to be defined on top of any multiaddr not just ones that end in /http" (as documented in #550)

[MarcoPolo]

Context for this issue is that Juan asked that we define a way to reference HTTP resources in multiaddrs sooner rather than later because:

• As soon as we introduce HTTP semantics to libp2p folks will want to reference HTTP resources in multiaddrs.
• HTTP resources can be defined outside of a specific protocol, so it's not enough to prefix them with a custom multicodec (as suggested in Document /http #550).

This introduces a new way of using Multiaddrs that we haven't seen much in practice (With the exception of IPNI's use of a custom multicodec httpath ipni/go-libipni#42). Multiaddrs have primarily been used as a way of describing how to reach a peer. With this, multiaddrs will describe how to reach a resource.

Prior discussion:
multiformats/multicodec#324
ipni/go-libipni#42

[MarcoPolo]

My current thinking is that /httpath (or /httppath, my preference) is a reasonable solution to this. This can be appended to any transport and defines where an HTTP resource exists and the transport used to address the peer that has this resource. More details here: ipni/go-libipni#42 (comment)

[MarcoPolo]

PR here: multiformats/multiaddr#164