Sync: Propagate block announcement data (#7903)

* Sync: Propagate block announcement data

This pr adds a feature to the sync protocol to propagate the data that
we received alongside a block announcement. This is done by adding a
cache that caches the last X block announcement data where X is set to
the number of `in_peers` (giving every peer the chance to send us a
different block). This will be required by parachains to ensure that
even peers who are not connected to a collator receive the data
alongside the block announcement to properly validate it and request the
block.

* Review comment

* Bring back the code and add new variant to ensure we don't insert block
announce data when something wasn't checked

* Also use out_peers

substrate/client/network-gossip/src/state_machine.rs

@@ -570,7 +570,7 @@ mod tests {
 			unimplemented!();
 		}
 
-		fn announce(&self, _: B::Hash, _: Vec<u8>) {
+		fn announce(&self, _: B::Hash, _: Option<Vec<u8>>) {
 			unimplemented!();
 		}
 	}