[feature]: Payment channel itest-driven deliverables

[dstadulis]

Is your feature request related to a problem? Please describe. Discover the necessary RPCs required for payment channel functionality between lnd and tapd. Exploratory work is included in https://github.com/lightninglabs/taproot-assets/tree/tap-channels-itest

Rough notes [Edit at will]

• [ ] Channel funding and commitments
• [ ] Uses 3 diff asset pieces which are signed individually
• [ ] Musig2 working
• [ ] Keep it as an itest
• [ ] Abstract in itests into RPC
• [ ] Add helper functions

Describe the solution you'd like

Describe alternatives you've considered

Additional context 🐇 37701f5ce21969e2e81fc027dc5f454d9d2633f1250369188e304d8cc6784395