Snowbridge v2 - Outbound Queue

[yrong]

Context

This PR is for implement the design in SnowbridgeV2, essentially moving from ordered messaging system to an unordered one.

It focus more on outbound changes, inbound changes will be addressed in another PR.

The point is that we want to make V2 work side by side with V1, so add new routes/pallets specific for V2 and leave legacy codes untouched is important.

This PR is also based on XCM V5 with new instructions like AliasOrigin, InitiateTransfer in place.

Initial PR yrong#4 has been internally reviewed, companion changes required for other components of the bridge including:

• Contract

• Relayer

Workflow

1. on AH we add a custom exporter returns a lower fee(without the execution cost on Ethereum including), essentially predict the route by content of XCM, more details in Predicate route table by Xcm #6074 and thanks for the review from @bkontur

2. On BH also add a new exporter to handle V2 specific xcm, convert the xcm to a Message structure which will be executed on Ethereum.

3. In OutboundQueue store the message into a Merkle tree as V1 before, and add the pending message with the fee attached into PendingOrder storage. Code here for detail. The off-chain relayer should check if relaying the message with the fee attached is profitable.

4. In OutboundQueue add a new extrinsic submit_delivery_proof in which we verify the Message has been delivered to Ethereum, only after that add the fee to RewardLeger which can be redeemed by the relayer later, more details in Relayer rewards paid to specified location account #6578

Review notes

Simulated test is the entry point how to build XCM for V2, also a good candidate to dig deep into the process.

cargo test -p bridge-hub-westend-integration-tests --lib tests::snowbridge_v2_outbound -- --nocapture