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/collator-protocol/src/collator_side/mod.rs

@@ -882,7 +882,7 @@ async fn handle_incoming_peer_message<Context>(
 	match msg {
 		Versioned::V1(V1::Declare(..)) |
 		Versioned::V2(V2::Declare(..)) |
-		Versioned::VStaging(V2::Declare(..)) => {
+		Versioned::V3(V2::Declare(..)) => {
 			gum::trace!(
 				target: LOG_TARGET,
 				?origin,
@@ -895,7 +895,7 @@ async fn handle_incoming_peer_message<Context>(
 		},
 		Versioned::V1(V1::AdvertiseCollation(_)) |
 		Versioned::V2(V2::AdvertiseCollation { .. }) |
-		Versioned::VStaging(V2::AdvertiseCollation { .. }) => {
+		Versioned::V3(V2::AdvertiseCollation { .. }) => {
 			gum::trace!(
 				target: LOG_TARGET,
 				?origin,
@@ -911,7 +911,7 @@ async fn handle_incoming_peer_message<Context>(
 		},
 		Versioned::V1(V1::CollationSeconded(relay_parent, statement)) |
 		Versioned::V2(V2::CollationSeconded(relay_parent, statement)) |
-		Versioned::VStaging(V2::CollationSeconded(relay_parent, statement)) => {
+		Versioned::V3(V2::CollationSeconded(relay_parent, statement)) => {
 			if !matches!(statement.unchecked_payload(), Statement::Seconded(_)) {
 				gum::warn!(
 					target: LOG_TARGET,

polkadot/node/network/collator-protocol/src/validator_side/mod.rs

@@ -777,7 +777,7 @@ async fn process_incoming_peer_message<Context>(
 	match msg {
 		Versioned::V1(V1::Declare(collator_id, para_id, signature)) |
 		Versioned::V2(V2::Declare(collator_id, para_id, signature)) |
-		Versioned::VStaging(V2::Declare(collator_id, para_id, signature)) => {
+		Versioned::V3(V2::Declare(collator_id, para_id, signature)) => {
 			if collator_peer_id(&state.peer_data, &collator_id).is_some() {
 				modify_reputation(
 					&mut state.reputation,
@@ -894,7 +894,7 @@ async fn process_incoming_peer_message<Context>(
 			candidate_hash,
 			parent_head_data_hash,
 		}) |
-		Versioned::VStaging(V2::AdvertiseCollation {
+		Versioned::V3(V2::AdvertiseCollation {
 			relay_parent,
 			candidate_hash,
 			parent_head_data_hash,
@@ -923,7 +923,7 @@ async fn process_incoming_peer_message<Context>(
 			},
 		Versioned::V1(V1::CollationSeconded(..)) |
 		Versioned::V2(V2::CollationSeconded(..)) |
-		Versioned::VStaging(V2::CollationSeconded(..)) => {
+		Versioned::V3(V2::CollationSeconded(..)) => {
 			gum::warn!(
 				target: LOG_TARGET,
 				peer_id = ?origin,