Description

Use the new Gateway Queue pallet in LP and LP gateway.

Changes and Descriptions

Use pallet-liquidity-pools-gateway-queue for queueing inbound and outbound message in the LP gateway.
Add new handler traits for inbound and outbound messages that are implemented by LP and LP gateway respectively.

[x] I have added Rust doc comments to structs, enums, traits and functions
[x] I have made corresponding changes to the documentation
[ ] I have performed a self-review of my code
[x] I have added tests that prove my fix is effective or that my feature works
[ ] Address the benchmark weight suggestion here
[x] Skip the LP gateway queue in as many integration tests as possible.
[x] Replace the fudge runtime with the normal runtime in the integration tests, where possible.