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/zombienet_tests/functional/0009-approval-voting-coalescing.toml

@@ -0,0 +1,115 @@
+[settings]
+timeout = 1000
+
+[relaychain]
+default_image = "{{ZOMBIENET_INTEGRATION_TEST_IMAGE}}"
+chain = "rococo-local"
+
+[relaychain.genesis.runtimeGenesis.patch.configuration.config]
+  needed_approvals = 4
+  relay_vrf_modulo_samples = 6
+
+[relaychain.genesis.runtimeGenesis.patch.configuration.config.approval_voting_params]
+  max_approval_coalesce_count = 5
+
+[relaychain.default_resources]
+limits = { memory = "4G", cpu = "2" }
+requests = { memory = "2G", cpu = "1" }
+
+  [[relaychain.node_groups]]
+  name = "alice"
+  args = [ "-lparachain=trace,runtime=debug" ]
+  count = 13
+
+[[parachains]]
+id = 2000
+addToGenesis = true
+genesis_state_generator = "undying-collator export-genesis-state --pov-size=100000 --pvf-complexity=1"
+
+  [parachains.collator]
+  name = "collator01"
+  image = "{{COL_IMAGE}}"
+  command = "undying-collator"
+  args = ["-lparachain=debug", "--pov-size=100000", "--pvf-complexity=1", "--parachain-id=2000"]
+
+[[parachains]]
+id = 2001
+addToGenesis = true
+genesis_state_generator = "undying-collator export-genesis-state --pov-size=100000 --pvf-complexity=10"
+
+  [parachains.collator]
+  name = "collator02"
+  image = "{{COL_IMAGE}}"
+  command = "undying-collator"
+  args = ["-lparachain=debug", "--pov-size=100000", "--parachain-id=2001", "--pvf-complexity=10"]
+
+[[parachains]]
+id = 2002
+addToGenesis = true
+genesis_state_generator = "undying-collator export-genesis-state --pov-size=100000 --pvf-complexity=100"
+
+  [parachains.collator]
+  name = "collator03"
+  image = "{{COL_IMAGE}}"
+  command = "undying-collator"
+  args = ["-lparachain=debug", "--pov-size=100000", "--parachain-id=2002", "--pvf-complexity=100"]
+
+[[parachains]]
+id = 2003
+addToGenesis = true
+genesis_state_generator = "undying-collator export-genesis-state --pov-size=20000 --pvf-complexity=300"
+
+  [parachains.collator]
+  name = "collator04"
+  image = "{{COL_IMAGE}}"
+  command = "undying-collator"
+  args = ["-lparachain=debug", "--pov-size=20000", "--parachain-id=2003", "--pvf-complexity=300"]
+
+[[parachains]]
+id = 2004
+addToGenesis = true
+genesis_state_generator = "undying-collator export-genesis-state --pov-size=100000 --pvf-complexity=300"
+
+  [parachains.collator]
+  name = "collator05"
+  image = "{{COL_IMAGE}}"
+  command = "undying-collator"
+  args = ["-lparachain=debug", "--pov-size=100000", "--parachain-id=2004", "--pvf-complexity=300"]
+
+[[parachains]]
+id = 2005
+addToGenesis = true
+genesis_state_generator = "undying-collator export-genesis-state --pov-size=20000 --pvf-complexity=400"
+
+  [parachains.collator]
+  name = "collator06"
+  image = "{{COL_IMAGE}}"
+  command = "undying-collator"
+  args = ["-lparachain=debug", "--pov-size=20000",  "--pvf-complexity=400", "--parachain-id=2005"]
+
+[[parachains]]
+id = 2006
+addToGenesis = true
+genesis_state_generator = "undying-collator export-genesis-state --pov-size=100000 --pvf-complexity=300"
+
+  [parachains.collator]
+  name = "collator07"
+  image = "{{COL_IMAGE}}"
+  command = "undying-collator"
+  args = ["-lparachain=debug", "--pov-size=100000",  "--pvf-complexity=300", "--parachain-id=2006"]
+
+[[parachains]]
+id = 2007
+addToGenesis = true
+genesis_state_generator = "undying-collator export-genesis-state --pov-size=100000 --pvf-complexity=300"
+
+  [parachains.collator]
+  name = "collator08"
+  image = "{{COL_IMAGE}}"
+  command = "undying-collator"
+  args = ["-lparachain=debug", "--pov-size=100000",  "--pvf-complexity=300", "--parachain-id=2007"]
+
+[types.Header]
+number = "u64"
+parent_hash = "Hash"
+post_state = "Hash"