Request based PoV distribution (#2640)

* Indentation fix.

* Prepare request-response for PoV fetching.

* Drop old PoV distribution.

* WIP: Fetch PoV directly from backing.

* Backing compiles.

* Runtime access and connection management for PoV distribution.

* Get rid of seemingly dead code.

* Implement PoV fetching.

Backing does not yet use it.

* Don't send `ConnectToValidators` for empty list.

* Even better - no need to check over and over again.

* PoV fetching implemented.

+ Typechecks
+ Should work

Missing:

- Guide
- Tests
- Do fallback fetching in case fetching from seconding validator fails.

* Check PoV hash upon reception.

* Implement retry of PoV fetching in backing.

* Avoid pointless validation spawning.

* Add jaeger span to pov requesting.

* Add back tracing.

* Review remarks.

* Whitespace.

* Whitespace again.

* Cleanup + fix tests.

* Log to log target in overseer.

* Fix more tests.

* Don't fail if group cannot be found.

* Simple test for PoV fetcher.

* Handle missing group membership better.

* Add test for retry functionality.

* Fix flaky test.

* Spaces again.

* Guide updates.

* Spaces.

polkadot/Cargo.lock

@@ -5627,6 +5627,7 @@ dependencies = [
  "sp-core",
  "sp-keyring",
  "sp-keystore",
+ "sp-tracing",
  "thiserror",
  "tracing",
 ]
@@ -5778,6 +5779,7 @@ dependencies = [
  "polkadot-primitives",
  "sc-network",
  "strum",
+ "thiserror",
 ]
 
 [[package]]
@@ -5926,25 +5928,6 @@ dependencies = [
  "thiserror",
 ]
 
-[[package]]
-name = "polkadot-pov-distribution"
-version = "0.1.0"
-dependencies = [
- "assert_matches",
- "env_logger 0.8.2",
- "futures 0.3.13",
- "log",
- "polkadot-node-network-protocol",
- "polkadot-node-subsystem",
- "polkadot-node-subsystem-test-helpers",
- "polkadot-node-subsystem-util",
- "polkadot-primitives",
- "sp-core",
- "sp-keyring",
- "thiserror",
- "tracing",
-]
-
 [[package]]
 name = "polkadot-primitives"
 version = "0.8.30"
@@ -6231,7 +6214,6 @@ dependencies = [
  "polkadot-node-subsystem-util",
  "polkadot-overseer",
  "polkadot-parachain",
- "polkadot-pov-distribution",
  "polkadot-primitives",
  "polkadot-rpc",
  "polkadot-runtime",