feat: USDS migration for xDAI bridge

[zengzengzenghuy]

What

Background: https://forum.gnosis.io/t/gip-118-should-sdai-be-replaced-by-susds-in-the-bridge/9354

How

1. New Router contract(BridgeRouter.sol) to route relayTokens function and claim token executeSignatuers to xDAI bridge or Omnibridge, or others in future upgrade
   1. Router contract is controlled by bridge governors and upgradeable
   2. Routes:
      1. DAI → XDaiBridgePeripheral
      2. USDS → XDaiBridge
      3. ETH →WETHOmnibridgeRouter
      4. Other tokens → Omnibridge
2. xDAI bridge only accepts deposit from USDS token.
   1. Function interfaces are not changed, but only changing the address of daiToken() to USDS and sDaiToken() to sUSDS.

New contracts

1. BridgeRouter: https://github.com/gnosischain/tokenbridge-contracts/blob/feat/xdai-usds-migration/contracts/upgradeable_contracts/erc20_to_native/BridgeRouter.sol , Upgradeable with TransparentUpgradeableProxy https://github.com/gnosischain/tokenbridge-contracts/blob/feat/xdai-usds-migration/contracts/upgradeability/TransparentUpgradeableProxy.sol
2. XDaiBridgePeripheral: https://github.com/gnosischain/tokenbridge-contracts/blob/feat/xdai-usds-migration/contracts/upgradeable_contracts/erc20_to_native/XDaiBridgePeripheral.sol

Modified contracts

1. XDaiForeignBridge: https://github.com/gnosischain/tokenbridge-contracts/blob/feat/xdai-usds-migration/contracts/upgradeable_contracts/erc20_to_native/XDaiForeignBridge.sol
2. SavingsDaiConnector: https://github.com/gnosischain/tokenbridge-contracts/blob/feat/xdai-usds-migration/contracts/upgradeable_contracts/erc20_to_native/SavingsDaiConnector.sol

Fork Test

https://github.com/gnosischain/tokenbridge-contracts/blob/feat/xdai-usds-migration/test/foundry/forkTest.sh

Bridge validator test (Check if bridge validator continues to work after bridge migration & xDAI can be still be minted on Gnosis Chain)

https://github.com/gnosischain/xdai-bridge-test