Batch messages to network bridge and introduce a timeout to SubsystemContext::send_message (#2197)

* guide: batch network messages

* bridge: batch

* av-dist: batch outgoing messages

* time-out message sends in subsystem context

* Update node/subsystem/src/messages.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Revert "time-out message sends in subsystem context"

This reverts commit d49be62557ec37c8a350b93718acad723df704ef.

* Update node/network/availability-distribution/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

polkadot/roadmap/implementers-guide/src/node/utility/network-bridge.md

@@ -86,11 +86,11 @@ Map the message onto the corresponding [Event Handler](#event-handlers) based on
 
 - Adjust peer reputation according to cost or benefit provided
 
-### SendValidationMessage
+### SendValidationMessage / SendValidationMessages
 
 - Issue a corresponding `ProtocolMessage` to each listed peer on the validation peer-set.
 
-### SendCollationMessage
+### SendCollationMessage / SendCollationMessages
 
 - Issue a corresponding `ProtocolMessage` to each listed peer on the collation peer-set.
 

polkadot/roadmap/implementers-guide/src/types/overseer-protocol.md

@@ -320,7 +320,11 @@ enum NetworkBridgeMessage {
 	/// Send a message to one or more peers on the validation peerset.
 	SendValidationMessage([PeerId], ValidationProtocolV1),
 	/// Send a message to one or more peers on the collation peerset.
-	SendCollationMessage([PeerId], ValidationProtocolV1),
+	SendCollationMessage([PeerId], CollationProtocolV1),
+	/// Send multiple validation messages.
+	SendValidationMessages([([PeerId, ValidationProtocolV1])]),
+	/// Send multiple collation messages.
+	SendCollationMessages([([PeerId, ValidationProtocolV1])]),
 	/// Connect to peers who represent the given `validator_ids`.
 	///
 	/// Also ask the network to stay connected to these peers at least