feature or demo: iroh-rpc over iroh

[rklaehn]

Remote control a node anywhere in the world via the rpc protocol transmitted via iroh-net.

This might actually be useful, but it would also be an example how to use a rather complex protocol over iroh-net.

The node would need a file with a set of "authorized keys" and would only accept rpc protocol connections from those.

Quic-rpc already has a quinn transport, which we use by default. We could easily extend it or make a dedicated iroh-net transport.