Snowbridge v2 - Outbound Queue

[yrong]

Context

This PR is for SnowbridgeV2, essentially unordered messaging system. This PR focus more on outbound changes, inbound changes will be addressed in another PR.

The point is that we want to make V1(i.e. ordered messaging) work side by side with V2, so we add new pallets without changing the legacy codes.

SnowbridgeV2 is based upon XCMV5 with new instructions like AliasOrigin, InitiateTransfer in place.

Initial PR yrong#4 which has been internally reviewed. It also requires some companion changes in:

• Contract

• Relayer

Workflow

1. Simulated test

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

is the entry point where we build XCM to start the cross-chain transfer from AH.

2. on AH we add a custom exporter returns a lower fee(without the execution cost on Ethereum comparing with V1) charged from the user when exporting with V2 specific instructions(i.e. AliasOrigin), essentially predict the route by content of XCM, more details in Predicate route table by Xcm #6074

3. On BH also add a new exporter to handle V2 specific xcm, convert XCM to Message structure which will be executed on Ethereum as following:

pub struct Message {
    /// Origin of the original sender from source chain
    pub origin: H256,
    /// ID of the message
    pub id: H256,
    /// Fee amount in WETH
    pub fee: u128, 
    /// Commands be executed on Ethereum
    pub commands: BoundedVec<Command, ConstU32<5>>,
}

4. In OutboundQueue encode the message and store it into a merkle tree as before, add the pending message into PendingOrder storage. Code here

5. In OutboundQueue add a new extrinsic submit_delivery_proof in which we verify the Message has been delivered to Ethereum, 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

It may still require further change/refactoring but would be great if we can get some early feedback.