subsystem for issuing background connection requests (#2538)

* initial subsystem for issuing connection requests

* finish the initial impl

* integrate with the overseer

* rename to gossip-support

* fix renamings leftover

* remove run_inner

* fix compilation

* random subset of sqrt

polkadot/node/subsystem/src/messages.rs

@@ -682,6 +682,11 @@ pub enum ApprovalDistributionMessage {
 	NetworkBridgeUpdateV1(NetworkBridgeEvent<protocol_v1::ApprovalDistributionMessage>),
 }
 
+/// Message to the Gossip Support subsystem.
+#[derive(Debug)]
+pub enum GossipSupportMessage {
+}
+
 /// A message type tying together all message types that are used across Subsystems.
 #[subsystem_dispatch_gen(NetworkBridgeEvent<protocol_v1::ValidationProtocol>)]
 #[derive(Debug, derive_more::From)]
@@ -735,6 +740,9 @@ pub enum AllMessages {
 	ApprovalVoting(ApprovalVotingMessage),
 	/// Message for the Approval Distribution subsystem.
 	ApprovalDistribution(ApprovalDistributionMessage),
+	/// Message for the Gossip Support subsystem.
+	#[skip]
+	GossipSupport(GossipSupportMessage),
 }
 
 impl From<IncomingRequest<req_res_v1::AvailabilityFetchingRequest>> for AllMessages {