BridgeRouter and AMB messaging system

[LayneHaber]

Description

For AMB related changes see: https://www.notion.so/connext/Interim-AMB-Messaging-f4690a794a984ac78e2504af062c4fea

Type of change

• [x] Docs change / dependency upgrade
• [x] Configuration / tooling changes
• [x] Refactoring
• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] Requires changes in customer code

High-level change(s) description - from the user's perspective

• Move all minting/burning, and custodying to nomad BridgeRouter
• Connext no longer needs to be a nomad router

Related Issue(s)

Fixes #1464

Related pull request(s)

See corresponding nomad PR