[CHECKLIST] Integrate native bridge between mainnet and parachain

[drewstone]

Overview

We want to have a native bridge between Tangle and Tangle parachain. One main reason is to move TNT between the chains as trustlessly as possible. Instead of relying on an external bridge like Sygma to handle sygTNT, etc. This will also allow us to control governance of the parachain from the main chain as well.

• https://github.com/paritytech/polkadot-sdk/tree/master/bridges

Checklist

• [ ] Research and open PR with new pallets. #706
• [ ] Relayer for relaying finality notifications to grandpa light client #707
• [ ] Research infrastructure requirements and document below.
• [ ] XCM support?
• [ ] Add test for asset transfers, governance messages (validate message from mainnet Origin).

More resources

• https://github.com/paritytech/polkadot-sdk/blob/master/bridges/docs/high-level-overview.md

[drewstone]

Open questions

1. What is the process for sending an asset from an arbitrary parachain to Tangle mainnet and depositing it? Is it possible in 1 transaction/XCM?
2. What is the process for withdrawing an asset from Tangle mainnet and sending it to Tangle parachain or another arbitrary parachain? Is it possible in 1 transaction/XCM?