Availability store subsystem (#1404)

* Initial commit

* WIP

* Make atomic transactions

* Remove pruning code

* Fix build and add a Nop to bridge

* Fixes from review

* Move config struct around for clarity

* Rename constructor and warn on missing docs

* Fix a test and rename a message

* Fix some more reviews

* Obviously failed to rebase cleanly

polkadot/Cargo.lock

@@ -4579,6 +4579,25 @@ dependencies = [
  "sp-runtime",
 ]
 
+[[package]]
+name = "polkadot-node-core-av-store"
+version = "0.1.0"
+dependencies = [
+ "assert_matches",
+ "derive_more 0.99.9",
+ "futures 0.3.5",
+ "kvdb",
+ "kvdb-memorydb",
+ "kvdb-rocksdb",
+ "log 0.4.8",
+ "parity-scale-codec",
+ "polkadot-erasure-coding",
+ "polkadot-node-subsystem",
+ "polkadot-overseer",
+ "polkadot-primitives",
+ "sp-core",
+]
+
 [[package]]
 name = "polkadot-node-core-backing"
 version = "0.1.0"