A fast-path for requesting AvailableData from backing validators (#2453)

* guide changes for a fast-path requesting from backing validators

* add backing group to availability recovery message

* add new phase to interaction

* typos

* add full data messages

* handle new network messages

* dispatch full data requests

* cleanup

* check chunk index

* test for invalid recovery

* tests

* Typos.

* fix some grumbles

* be more explicit about error handling and control flow

* fast-path param

* use with_chunks_only in Service

Co-authored-by: Robert Klotzner <robert.klotzner@gmx.at>

polkadot/node/overseer/src/lib.rs

@@ -2726,6 +2726,7 @@ mod tests {
 		AvailabilityRecoveryMessage::RecoverAvailableData(
 			Default::default(),
 			Default::default(),
+			None,
 			sender,
 		)
 	}