impl approval distribution (#2160)

* initial impl approval distribution

* initial tests and fixes

* batching seems difficult: different peers have different needs

* bridge: fix test after merge

* some guide updates

* only send assignments to peers who know about the block

* fix a test, add approvals test

* simplify

* do not send assignment to peers for finalized blocks

* guide: protocol input and output

* one more test

* more comments, logs, initial metrics

* fix a typo

* one more thing: early return when reimporting a thing locally

polkadot/Cargo.lock

@@ -4884,6 +4884,27 @@ dependencies = [
  "thiserror",
 ]
 
+[[package]]
+name = "polkadot-approval-distribution"
+version = "0.1.0"
+dependencies = [
+ "assert_matches",
+ "env_logger 0.8.2",
+ "futures 0.3.12",
+ "log",
+ "polkadot-node-network-protocol",
+ "polkadot-node-primitives",
+ "polkadot-node-subsystem",
+ "polkadot-node-subsystem-test-helpers",
+ "polkadot-node-subsystem-util",
+ "polkadot-primitives",
+ "rand_core 0.5.1",
+ "schnorrkel",
+ "sp-core",
+ "tracing",
+ "tracing-futures",
+]
+
 [[package]]
 name = "polkadot-availability-bitfield-distribution"
 version = "0.1.0"
@@ -5289,6 +5310,7 @@ dependencies = [
  "parity-scale-codec",
  "polkadot-primitives",
  "polkadot-statement-table",
+ "sp-consensus-slots",
  "sp-consensus-vrf",
  "sp-core",
  "sp-runtime",
@@ -5683,6 +5705,7 @@ dependencies = [
  "pallet-im-online",
  "pallet-staking",
  "pallet-transaction-payment-rpc-runtime-api",
+ "polkadot-approval-distribution",
  "polkadot-availability-bitfield-distribution",
  "polkadot-availability-distribution",
  "polkadot-availability-recovery",