Approve multiple candidates with a single signature (#1191)

Initial implementation for the plan discussed here: https://github.com/paritytech/polkadot-sdk/issues/701
Built on top of https://github.com/paritytech/polkadot-sdk/pull/1178
v0: https://github.com/paritytech/polkadot/pull/7554,

## Overall idea

When approval-voting checks a candidate and is ready to advertise the
approval, defer it in a per-relay chain block until we either have
MAX_APPROVAL_COALESCE_COUNT candidates to sign or a candidate has stayed
MAX_APPROVALS_COALESCE_TICKS in the queue, in both cases we sign what
candidates we have available.

This should allow us to reduce the number of approvals messages we have
to create/send/verify. The parameters are configurable, so we should
find some values that balance:

- Security of the network: Delaying broadcasting of an approval
shouldn't but the finality at risk and to make sure that never happens
we won't delay sending a vote if we are past 2/3 from the no-show time.
- Scalability of the network: MAX_APPROVAL_COALESCE_COUNT = 1 &
MAX_APPROVALS_COALESCE_TICKS =0, is what we have now and we know from
the measurements we did on versi, it bottlenecks
approval-distribution/approval-voting when increase significantly the
number of validators and parachains
- Block storage: In case of disputes we have to import this votes on
chain and that increase the necessary storage with
MAX_APPROVAL_COALESCE_COUNT * CandidateHash per vote. Given that
disputes are not the normal way of the network functioning and we will
limit MAX_APPROVAL_COALESCE_COUNT in the single digits numbers, this
should be good enough. Alternatively, we could try to create a better
way to store this on-chain through indirection, if that's needed.

## Other fixes:
- Fixed the fact that we were sending random assignments to
non-validators, that was wrong because those won't do anything with it
and they won't gossip it either because they do not have a grid topology
set, so we would waste the random assignments.
- Added metrics to be able to debug potential no-shows and
mis-processing of approvals/assignments.

## TODO:
- [x] Get feedback, that this is moving in the right direction. @ordian
@sandreim @eskimor @burdges, let me know what you think.
- [x] More and more testing.
- [x]  Test in versi.
- [x] Make MAX_APPROVAL_COALESCE_COUNT &
MAX_APPROVAL_COALESCE_WAIT_MILLIS a parachain host configuration.
- [x] Make sure the backwards compatibility works correctly
- [x] Make sure this direction is compatible with other streams of work:
https://github.com/paritytech/polkadot-sdk/issues/635 &
https://github.com/paritytech/polkadot-sdk/issues/742
- [x] Final versi burn-in before merging

---------

Signed-off-by: Alexandru Gheorghe <alexandru.gheorghe@parity.io>

polkadot/node/network/bitfield-distribution/src/lib.rs

@@ -32,7 +32,7 @@ use polkadot_node_network_protocol::{
 		GridNeighbors, RandomRouting, RequiredRouting, SessionBoundGridTopologyStorage,
 	},
 	peer_set::{ProtocolVersion, ValidationVersion},
-	v1 as protocol_v1, v2 as protocol_v2, vstaging as protocol_vstaging, OurView, PeerId,
+	v1 as protocol_v1, v2 as protocol_v2, v3 as protocol_v3, OurView, PeerId,
 	UnifiedReputationChange as Rep, Versioned, View,
 };
 use polkadot_node_subsystem::{
@@ -102,8 +102,8 @@ impl BitfieldGossipMessage {
 					self.relay_parent,
 					self.signed_availability.into(),
 				)),
-			Some(ValidationVersion::VStaging) =>
-				Versioned::VStaging(protocol_vstaging::BitfieldDistributionMessage::Bitfield(
+			Some(ValidationVersion::V3) =>
+				Versioned::V3(protocol_v3::BitfieldDistributionMessage::Bitfield(
 					self.relay_parent,
 					self.signed_availability.into(),
 				)),
@@ -503,8 +503,8 @@ async fn relay_message<Context>(
 		let v2_interested_peers =
 			filter_by_peer_version(&interested_peers, ValidationVersion::V2.into());
 
-		let vstaging_interested_peers =
-			filter_by_peer_version(&interested_peers, ValidationVersion::VStaging.into());
+		let v3_interested_peers =
+			filter_by_peer_version(&interested_peers, ValidationVersion::V3.into());
 
 		if !v1_interested_peers.is_empty() {
 			ctx.send_message(NetworkBridgeTxMessage::SendValidationMessage(
@@ -522,10 +522,10 @@ async fn relay_message<Context>(
 			.await
 		}
 
-		if !vstaging_interested_peers.is_empty() {
+		if !v3_interested_peers.is_empty() {
 			ctx.send_message(NetworkBridgeTxMessage::SendValidationMessage(
-				vstaging_interested_peers,
-				message.into_validation_protocol(ValidationVersion::VStaging.into()),
+				v3_interested_peers,
+				message.into_validation_protocol(ValidationVersion::V3.into()),
 			))
 			.await
 		}
@@ -551,7 +551,7 @@ async fn process_incoming_peer_message<Context>(
 			relay_parent,
 			bitfield,
 		)) |
-		Versioned::VStaging(protocol_vstaging::BitfieldDistributionMessage::Bitfield(
+		Versioned::V3(protocol_v3::BitfieldDistributionMessage::Bitfield(
 			relay_parent,
 			bitfield,
 		)) => (relay_parent, bitfield),