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/runtime/parachains/src/configuration.rs

@@ -26,8 +26,9 @@ use polkadot_parachain_primitives::primitives::{
 	MAX_HORIZONTAL_MESSAGE_NUM, MAX_UPWARD_MESSAGE_NUM,
 };
 use primitives::{
-	vstaging::NodeFeatures, AsyncBackingParams, Balance, ExecutorParamError, ExecutorParams,
-	SessionIndex, LEGACY_MIN_BACKING_VOTES, MAX_CODE_SIZE, MAX_HEAD_DATA_SIZE, MAX_POV_SIZE,
+	vstaging::{ApprovalVotingParams, NodeFeatures},
+	AsyncBackingParams, Balance, ExecutorParamError, ExecutorParams, SessionIndex,
+	LEGACY_MIN_BACKING_VOTES, MAX_CODE_SIZE, MAX_HEAD_DATA_SIZE, MAX_POV_SIZE,
 	ON_DEMAND_DEFAULT_QUEUE_MAX_SIZE,
 };
 use sp_runtime::{traits::Zero, Perbill};
@@ -263,6 +264,8 @@ pub struct HostConfiguration<BlockNumber> {
 	pub minimum_backing_votes: u32,
 	/// Node features enablement.
 	pub node_features: NodeFeatures,
+	/// Params used by approval-voting
+	pub approval_voting_params: ApprovalVotingParams,
 }
 
 impl<BlockNumber: Default + From<u32>> Default for HostConfiguration<BlockNumber> {
@@ -308,6 +311,7 @@ impl<BlockNumber: Default + From<u32>> Default for HostConfiguration<BlockNumber
 			pvf_voting_ttl: 2u32.into(),
 			minimum_validation_upgrade_delay: 2.into(),
 			executor_params: Default::default(),
+			approval_voting_params: ApprovalVotingParams { max_approval_coalesce_count: 1 },
 			on_demand_queue_max_size: ON_DEMAND_DEFAULT_QUEUE_MAX_SIZE,
 			on_demand_base_fee: 10_000_000u128,
 			on_demand_fee_variability: Perbill::from_percent(3),
@@ -515,7 +519,8 @@ pub mod pallet {
 	/// v7-v8:  <https://github.com/paritytech/polkadot/pull/6969>
 	/// v8-v9:  <https://github.com/paritytech/polkadot/pull/7577>
 	/// v9-v10: <https://github.com/paritytech/polkadot-sdk/pull/2177>
-	const STORAGE_VERSION: StorageVersion = StorageVersion::new(10);
+	/// v10-11: <https://github.com/paritytech/polkadot-sdk/pull/1191>
+	const STORAGE_VERSION: StorageVersion = StorageVersion::new(11);
 
 	#[pallet::pallet]
 	#[pallet::storage_version(STORAGE_VERSION)]
@@ -1191,6 +1196,7 @@ pub mod pallet {
 				config.on_demand_ttl = new;
 			})
 		}
+
 		/// Set the minimum backing votes threshold.
 		#[pallet::call_index(52)]
 		#[pallet::weight((
@@ -1203,6 +1209,7 @@ pub mod pallet {
 				config.minimum_backing_votes = new;
 			})
 		}
+
 		/// Set/Unset a node feature.
 		#[pallet::call_index(53)]
 		#[pallet::weight((
@@ -1220,6 +1227,22 @@ pub mod pallet {
 				config.node_features.set(index, value);
 			})
 		}
+
+		/// Set approval-voting-params.
+		#[pallet::call_index(54)]
+		#[pallet::weight((
+			T::WeightInfo::set_config_with_executor_params(),
+			DispatchClass::Operational,
+		))]
+		pub fn set_approval_voting_params(
+			origin: OriginFor<T>,
+			new: ApprovalVotingParams,
+		) -> DispatchResult {
+			ensure_root(origin)?;
+			Self::schedule_config_update(|config| {
+				config.approval_voting_params = new;
+			})
+		}
 	}
 
 	#[pallet::hooks]