This diff introduces a new `getavaproofs` message, which which requests for an `avaproofs` message containing all the proofs short ids from the peer.
Notes:
- The name does not contain the "compact" mention like one might expect, due to the limitation in the command name to 12 chars.
- There is a theoretical limit of 21 millions proofs which could cause the node to generate a oversized message (limited to 2MiB). This will be taken care in a follow-up.
Depends on D11454.