Enhance channel handling endpoint

[fusion44]

• [ ] support push sats to the peer during opening
• [ ] support setting a fee rate in addition to target confirmation
  • [ ] improve documentation, especially explain the difference between CLN and LND fee rates. See send coins for example.
• [ ] use a Request body instead of query parameters
• [ ] support opening private channels
• [ ] list-channels should return the current channel status. E.d opening, closing, etc

CLN: https://lightning.readthedocs.io/lightning-fundchannel.7.html

LND: https://api.lightning.community/#openchannel

[fusion44]

See #199