[Feature request] Add possibility to select specific channel for outgoing payment

[Darth-Coin]

Let's say we have this case. A small merchant using SBW, opened a HC, received some funds. Also have a normal channel with Thor/Bitrefill, with half of the funds on local balance. What about if the merchant want to move onchain, through a 3rd party service, some funds from a specific channel? Or just pay a LN invoice? Maybe is having a channel with more local balance and want to make space to receive more. Or just move a specific amount from HC to normal channel, NOT draining it.