Introduce bridge relayers pallet (#1513)

* introduce relayers pallet

* add MessageDeliveryAndDispatchPaymentAdapter

* plug in pallet into test runtimes

* tests prototype

* tests for the relayers pallet

* tests for payment adapter

* mint_reward_payment_procedure_actually_mints_tokens

* benchmarks

* remove irrelevant todo

* remove redundant clone

bridges/bin/rialto/runtime/src/lib.rs

@@ -389,6 +389,13 @@ impl pallet_authority_discovery::Config for Runtime {
 	type MaxAuthorities = MaxAuthorities;
 }
 
+impl pallet_bridge_relayers::Config for Runtime {
+	type Event = Event;
+	type Reward = Balance;
+	type PaymentProcedure = bp_relayers::MintReward<pallet_balances::Pallet<Runtime>, AccountId>;
+	type WeightInfo = ();
+}
+
 parameter_types! {
 	/// This is a pretty unscientific cap.
 	///
@@ -447,7 +454,12 @@ impl pallet_bridge_messages::Config<WithMillauMessagesInstance> for Runtime {
 
 	type TargetHeaderChain = crate::millau_messages::Millau;
 	type LaneMessageVerifier = crate::millau_messages::ToMillauMessageVerifier;
-	type MessageDeliveryAndDispatchPayment = ();
+	type MessageDeliveryAndDispatchPayment =
+		pallet_bridge_relayers::MessageDeliveryAndDispatchPaymentAdapter<
+			Runtime,
+			WithMillauMessagesInstance,
+			GetDeliveryConfirmationTransactionFee,
+		>;
 	type OnMessageAccepted = ();
 	type OnDeliveryConfirmed = ();
 
@@ -484,6 +496,7 @@ construct_runtime!(
 		MmrLeaf: pallet_beefy_mmr::{Pallet, Storage},
 
 		// Millau bridge modules.
+		BridgeRelayers: pallet_bridge_relayers::{Pallet, Call, Storage, Event<T>},
 		BridgeMillauGrandpa: pallet_bridge_grandpa::{Pallet, Call, Storage},
 		BridgeMillauMessages: pallet_bridge_messages::{Pallet, Call, Storage, Event<T>, Config<T>},