Channels: add hidden AbandonChannel functionality

[kaloudis]

Sometimes channels need to be abandoned if the funding inputs are double spent and not detected due to Neutrino sync issues. Other times you may want to abandon a trusted channel.

We should add the functionality but tucked way deeply on the Channel view. It has to be tucked away like a SNES cheat code so users don't accidentally shoot themselves in the foot and abandon channels without understanding the consequences.

[kaloudis]

https://lightning.engineering/api-docs/api/lnd/lightning/abandon-channel/index.html

This would also require us to build LND with devrpc tags