Implement the getpeerinfo RPC

[teor2345]

Motivation

Some mining pools use the getpeerinfo RPC to make sure the mining pool is still connected to peers.

Specifications

https://zcash.github.io/rpc/getpeerinfo.html

Designs

• Pass the shared zebra-network address book to the RPC server
• Call address_book.recently_live_peers() to get the peers that were recently connected
  • The shared address book is protected by a mutex, so we want to clone it to drop the mutex as soon as possible.
  • Doing the mutex lock and clone in a separate function will make sure this happens.
• Turn the list of MetaAddrs into a list of peerinfo records

We just need to provide the addr field for now, we can add more fields if mining pools ask for them.

[mpguerra]

We should implement these, however since they are not strictly mining RPCs they don't fall within the scope of the MVP.

[teor2345]

We should implement these, however since they are not strictly mining RPCs they don't fall within the scope of the MVP.

Some mining pools won't be able to use Zebra until we implement these RPCs.

[mpguerra]

@arya2 can we get an estimate here please?