Backend agent for relaying RPC requests to provider ships

[hanfel-dovned]

Backend side of "Updates to the Urbit x BOS stack that replace all RPC calls done via HTTP with an Urbit-native solution"

[hanfel-dovned]

The default way of doing this is for planets to send RPC requests through Ames to their star, which will forward them to their sidecar, and then respond over Ames.

An easier way would be for planets to request the URL of the star's RPC node from the star, and then just submit requests directly to the URL. The downside is that this might be trickier to permission. We want stars to be able to sell RPC access.