Handle pay-to-self payments

[TheBlueMatt]

For custodial multi-user walles, seeing an invoice that pays to self should generally be handled as if it were a "real" payment" - generate payment sent/received events like normal. We were generally relying on users to implement this themselves (as its kinda strange for a non-custodial wallet to do this), but it turns out its easy to screw up. Specifically, LNBits screwed up their pay-to-self payments [1] and allowed underpayment, and its largely the "obvious" way to implement it, so I wouldn't be surprised if some of our users screwed it up eventually too. Worth considering handling it for users (maybe with a config option).

[1] https://lists.linuxfoundation.org/pipermail/lightning-dev/2023-June/003983.html

[wpaulino]

Duplicate of #2462