Approval Distribution Subsystem (#1951)

* skeleton flow control

* tweaks & rename to approvals distribution

* Update roadmap/implementers-guide/src/node/approval/approval-distribution.md

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* Update roadmap/implementers-guide/src/node/approval/approval-distribution.md

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

* add a `NewBlocks` message and dispatch

* new data format for approval distribution

* guide: update view to include finalized block number

* approvals: document view updating

* pruning when peers disconnect

* add remaining message types

* fix link

* network message type

* handle incoming assignments

* import_and_circulate_approval

* handle new blocks

* address review comments

* address review comments and use nifty VRFProof

Co-authored-by: Peter Goodspeed-Niklaus <coriolinus@users.noreply.github.com>

polkadot/roadmap/implementers-guide/src/SUMMARY.md

@@ -8,7 +8,6 @@
 - [Architecture Overview](architecture.md)
   - [Messaging Overview](messaging.md)
 - [Runtime Architecture](runtime/README.md)
-  - [ApprovalsInherent Module](runtime/approvals_inherent.md)
   - [Initializer Module](runtime/initializer.md)
   - [Configuration Module](runtime/configuration.md)
   - [Disputes Module](runtime/disputes.md)
@@ -48,7 +47,7 @@
     - [Bitfield Signing](node/availability/bitfield-signing.md)
   - [Approval Subsystems](node/approval/README.md)
     - [Approval Voting](node/approval/approval-voting.md)
-    - [Approval Networking](node/approval/approval-networking.md)
+    - [Approval Distribution](node/approval/approval-distribution.md)
     - [Dispute Participation](node/approval/dispute-participation.md)
   - [Utility Subsystems](node/utility/README.md)
     - [Availability Store](node/utility/availability-store.md)