Do not run unneeded subsystems on collator and its alongside node (#3061)

Currently, collators and their alongside nodes spin up a full-scale
overseer running a bunch of subsystems that are not needed if the node
is not a validator. That was considered to be harmless; however, we've
got problems with unused subsystems getting stalled for a reason not
currently known, resulting in the overseer exiting and bringing down the
whole node.

This PR aims to only run needed subsystems on such nodes, replacing the
rest with `DummySubsystem`.

It also enables collator-optimized availability recovery subsystem
implementation.

Partially solves #1730.

cumulus/test/service/src/lib.rs

@@ -271,6 +271,7 @@ async fn build_relay_chain_interface(
 				polkadot_service::IsParachainNode::Collator(CollatorPair::generate().0)
 			},
 			None,
+			polkadot_service::CollatorOverseerGen,
 		)
 		.map_err(|e| RelayChainError::Application(Box::new(e) as Box<_>))?,
 		cumulus_client_cli::RelayChainMode::ExternalRpc(rpc_target_urls) =>