alternate availability store schema (#2237)

* alternate availability store schema

* improvements

* tweaks

* new DB schema and skeleton

* expand skeleton and tweaks

* handle backing and inclusion

* let finality be handled later

* handle finalized blocks

* implement query methods

* implement chunk storing

* StoreAvailableData

* fix an off-by-one

* implement pruning

* reinstate subsystem trait impl

* reinstate metrics

* fix warnings

* remove chunks_cache

* oops

* actually store the available data

* mockable pruning interval

* fix tests

* spacing

* fix code grumbles

* guide improvements

* make time mockable

* implement a mocked clock for testing

* return DB errors

* Update node/core/av-store/Cargo.toml

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Update roadmap/implementers-guide/src/node/utility/availability-store.md

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Update roadmap/implementers-guide/src/node/utility/availability-store.md

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* review grumbles & clarity

* fix review grumbles

* Add docs

Co-authored-by: Andronik Ordian <write@reusable.software>

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
Co-authored-by: Andronik Ordian <write@reusable.software>

polkadot/Cargo.lock

@@ -5044,6 +5044,7 @@ name = "polkadot-node-core-av-store"
 version = "0.1.0"
 dependencies = [
  "assert_matches",
+ "bitvec",
  "env_logger 0.8.2",
  "futures 0.3.8",
  "futures-timer 3.0.2",
@@ -5052,6 +5053,7 @@ dependencies = [
  "kvdb-rocksdb",
  "log",
  "parity-scale-codec",
+ "parking_lot 0.11.1",
  "polkadot-erasure-coding",
  "polkadot-node-subsystem",
  "polkadot-node-subsystem-test-helpers",
@@ -5060,6 +5062,7 @@ dependencies = [
  "polkadot-primitives",
  "sc-service",
  "sp-core",
+ "sp-keyring",
  "thiserror",
  "tracing",
  "tracing-futures",