Beefy on-demand justifications as a custom RequestResponse protocol (#12124)

* client/beefy: create communication module and move gossip there

* client/beefy: move beefy_protocol_name module to communication

* client/beefy: move notification module under communication

* client/beefy: add incoming request_response protocol handler

* client/beefy: keep track of connected peers and their progress

* client/beefy: add logic for generating Justif requests

* client/beefy: cancel outdated on-demand justification requests

* try Andre's suggestion for JustificationEngine

* justif engine add justifs validation

* client/beefy: impl OnDemandJustificationsEngine async next()

* move beefy proto name test

* client/beefy: initialize OnDemandJustificationsEngine

* client/tests: allow for custom req-resp protocols

* client/beefy: on-demand-justif: implement simple peer selection strategy

* client/beefy: fix voter initialization

Fix corner case where voter gets a single burst of finality
notifications just when it starts.

The notification stream was consumed by "wait_for_pallet" logic,
then main loop would subscribe to finality notifications, but by that
time some notifications might've been lost.

Fix this by subscribing the main loop to notifications before waiting
for pallet to become available. Share the same stream with the main loop
so that notifications for blocks before pallet available are ignored,
while _all_ notifications after pallet available are processed.

Add regression test for this.

Signed-off-by: acatangiu <[email protected]>

* client/beefy: make sure justif requests are always out for mandatory blocks

* client/beefy: add test for on-demand justifications sync

* client/beefy: tweak main loop event processing order

* client/beefy: run on-demand-justif-handler under same async task as voter

* client/beefy: add test for known-peers

* client/beefy: reorg request-response module

* client/beefy: add issue references for future work todos

* client/beefy: consolidate on-demand-justifications engine state machine

Signed-off-by: acatangiu <[email protected]>

* client/beefy: fix for polkadot companion

* client/beefy: implement review suggestions

* cargo fmt and clippy

* fix merge damage

* fix rust-doc

* fix merge damage

* fix merge damage

* client/beefy: add test for justif proto name

Signed-off-by: acatangiu <[email protected]>