pay dispatch fee at target chain (#911)

* pay dispatch fee at target chain

* refund unspent dispatch weight to messages relayer

* test that transfer actually happens

* pay-at-target-cchain benchmarks + fix previous benchmarks (invalid signature)

* include/exclude pay-dispatch-fee weight from delivery_and_dispatch_fee/delivery tx cost

* remvoe some redundant traces

* enum DispatchFeePayment {}

* typo

* update docs

* (revert removal of valid check)

* Update modules/messages/src/benchmarking.rs

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Update modules/messages/src/benchmarking.rs

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Update modules/messages/src/benchmarking.rs

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Update modules/messages/src/benchmarking.rs

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

Co-authored-by: Tomasz Drwięga <tomusdrw@users.noreply.github.com>
Co-authored-by: Tomasz Drwięga <tomasz@parity.io>

bridges/relays/bin-substrate/src/cli/send_message.rs

@@ -22,6 +22,7 @@ use crate::cli::{
 	TargetSigningParams,
 };
 use bp_message_dispatch::{CallOrigin, MessagePayload};
+use bp_runtime::messages::DispatchFeePayment;
 use codec::Encode;
 use frame_support::{dispatch::GetDispatchInfo, weights::Weight};
 use relay_substrate_client::{Chain, TransactionSignScheme};
@@ -211,6 +212,7 @@ where
 		spec_version,
 		weight,
 		origin,
+		dispatch_fee_payment: DispatchFeePayment::AtSourceChain,
 		call: HexBytes::encode(call),
 	};
 
@@ -222,12 +224,14 @@ where
 		spec_version,
 		weight,
 		origin,
+		dispatch_fee_payment,
 		call,
 	} = payload;
 	MessagePayload {
 		spec_version,
 		weight,
 		origin,
+		dispatch_fee_payment,
 		call: call.0,
 	}
 }
@@ -268,6 +272,7 @@ mod tests {
 				spec_version: relay_millau_client::Millau::RUNTIME_VERSION.spec_version,
 				weight: 1345000,
 				origin: CallOrigin::SourceAccount(sp_keyring::AccountKeyring::Alice.to_account_id()),
+				dispatch_fee_payment: DispatchFeePayment::AtSourceChain,
 				call: hex!("0401081234").to_vec(),
 			}
 		);
@@ -311,6 +316,7 @@ mod tests {
 					sp_keyring::AccountKeyring::Bob.into(),
 					signature,
 				),
+				dispatch_fee_payment: DispatchFeePayment::AtSourceChain,
 				call: hex!("0701081234").to_vec(),
 			}
 		);