Rust HTTP Rendezvous Server

Like https://github.com/matrix-org/node-http-rendezvous-server but in Rust

An implementation of MSC3886: Simple rendezvous capability that can be used standalone or packaged as a Synapse module.

Functionality constraints:

• the in progress rendezvous do not need to be persisted between server restarts
• the server does not need to work in a clustered/sharded deployment
• no authentication is needed for use of the server