Reduce network bandwidth, improve parablock times: optimize approval-distribution (#5164)

* gossip-support: be explicit about dimensions

* some guide updates

* update network-bridge to distinguish x and y dimensions

* get everything to compile

* beginnings

* some TODOs

* polkadot runtime: use relevant_authorities

* make gossip topologies per-session

* better formatting

* gossip support: use current session validators

* expand in comment

* adjust tests and fix index bug

* add past/present/future connection test and clean up code

* fmt

* network bridge: updated types

* update protocols to new gossip topology message

* guide updates

* add session to BlockApprovalMeta

* add session to block info

* refactor knowledge and remove most unify logic

* start replacing gossip_peers with new SessionTopologies

* add routing information to message state

* add some utilities to SessionTopology

* implement new gossip topology logic

* re-implement unify_with_peer

* distribute assignments according to topology

* finish grid topology implementation

* refactor network bridge slightly

* issue connection requests on all past/present/future

* fmt

* address grumbles

* tighten invariants in unify_with_peer

* implement random propagation

* refactor: extract required routing adjustment logic

* some block-age logic

* aggressively propagate messages when finality is slow

* overhaul aggression system to have 3 levels

* add aggression metrics

* remove aggression L3

* reduce random circulation

* remove PeerData

* get approval tests compiling

* use btree_map in known_by to make deterministic

* Revert "use btree_map in known_by to make deterministic"

This reverts commit 330d65343a7bb6fe4dd0f24bd8dbc15c0cbdbd9d.

* test XY grid propagation

* remove stray println

* test unshared dimension propagation

* add random gossip check

* test unify_with_peer better

* test sending after getting gossip topology

* test L1 aggression on originator

* test L1 aggression for non-originators

* test non-originator aggression L2

* fnt

* ~spellcheck

* fix statement-distribution tests

* fix flaky test

* fix metrics typo

* re-send periodically

* test resending

* typo

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>

* add more metrics about apd messages

* add back unify_with_peer logs

* make Resend an enum

* be more explicit when resending

* fmt

* fix error

* add a TODO for refactoring

* remove debug metrics

* add some guide stuff

* fmt

* update runtime API in test-runtim

Co-authored-by: Bernhard Schuster <bernhard@ahoi.io>