This plugin adds the ability to pay a bolt11 invoice through a specific channel,
even if a better/cheaper route exists through a different channel. A new RPC,
paythrough, is defined which takes the same arguments as pay, except the
second argument is scid which is the short-channel-id of the channel you wish
to pay through. This leverages the exclude argument on pay, so that argument
is removed.
This can be useful for keeping channels balanced or otherwise managing liquidity when you will be paying for something through lightning anyways.