Custom relay strategy (#1198)

* Add relayer strategy

* Add default relayer strategy

* default relayer strategy

* expose relayer strategy

* fix compile

* fix compile

* docs

* Rename Relayer to Relay, keep RelayerDecide

* split `DefaultRelayerStrategy` into `AltruisticRelayerStrategy` and `RationalRelayerStrategy`

* Remove relayer mode

* Remove unused import

* Rename `RelayerStrategy` to `RelayStrategy`

* Add missing docs

* clippy

* clippy

* clippy

* clippy

* Revert `relayer_mode` and add `MixStrategy`

* Add `EnforcementStrategy`

* fix bug and simplify relay strategy

* Update message_lane_loop.rs

* Update messages_target.rs

* clippy

* clippy

* clippy

* clippy

* clippy

* clippy

* clippy

* fix test

* fix test

* test

test

test

fix test

bridges/relays/bin-substrate/src/chains/polkadot_messages_to_kusama.rs

@@ -24,7 +24,7 @@ use sp_core::{Bytes, Pair};
 use bp_messages::MessageNonce;
 use bridge_runtime_common::messages::target::FromBridgedChainMessagesProof;
 use frame_support::weights::Weight;
-use messages_relay::message_lane::MessageLane;
+use messages_relay::{message_lane::MessageLane, relay_strategy::MixStrategy};
 use relay_kusama_client::{
 	HeaderId as KusamaHeaderId, Kusama, SigningParams as KusamaSigningParams,
 };
@@ -176,7 +176,13 @@ type KusamaTargetClient = SubstrateMessagesTarget<PolkadotMessagesToKusama>;
 
 /// Run Polkadot-to-Kusama messages sync.
 pub async fn run(
-	params: MessagesRelayParams<Polkadot, PolkadotSigningParams, Kusama, KusamaSigningParams>,
+	params: MessagesRelayParams<
+		Polkadot,
+		PolkadotSigningParams,
+		Kusama,
+		KusamaSigningParams,
+		MixStrategy,
+	>,
 ) -> anyhow::Result<()> {
 	let stall_timeout = relay_substrate_client::bidirectional_transaction_stall_timeout(
 		params.source_transactions_mortality,
@@ -222,14 +228,12 @@ pub async fn run(
 			Max messages in single transaction: {}\n\t\
 			Max messages size in single transaction: {}\n\t\
 			Max messages weight in single transaction: {}\n\t\
-			Relayer mode: {:?}\n\t\
 			Tx mortality: {:?}/{:?}\n\t\
 			Stall timeout: {:?}",
 		lane.message_lane.relayer_id_at_source,
 		max_messages_in_single_batch,
 		max_messages_size_in_single_batch,
 		max_messages_weight_in_single_batch,
-		params.relayer_mode,
 		params.source_transactions_mortality,
 		params.target_transactions_mortality,
 		stall_timeout,
@@ -257,7 +261,7 @@ pub async fn run(
 				max_messages_in_single_batch,
 				max_messages_weight_in_single_batch,
 				max_messages_size_in_single_batch,
-				relayer_mode: params.relayer_mode,
+				relay_strategy: params.relay_strategy,
 			},
 		},
 		PolkadotSourceClient::new(