[Feature] 1 invoice for 2 (or more)

### Feature description

An invoice is attached to a single person, so if I want to pay A and B, first A creates an invoice and sends to me and B does the same thing (then I pay).

This has this problem:

- I can't guarantee that either both will receive or none will receive, paying A could be successful but paying B could fail, forcing me to do a pay retry with B

This could be understood as a database transaction feature, where everything works thus is saved in the database or nothing works thus is not saved into the database.

### Describe the solution

A solution to this would be to make an invoice based in 2 or even more lightning addresses, that when paid, calculates the percentage for each one and attempts to pay both.

So when you decode the invoice, A gets 20% of the total amount and B 80% of the total amount.

### Describe alternatives

Currently I need to do it manually but it's not elegant.

### Additional context

_No response_

### Are you working on this?

None

The issue names no files, tests, or entry points. Start by mapping the existing invoice and Lightning-address payment flow, then clarify atomic failure behavior and percentage allocation; done requires an agreed design and tests covering multi-recipient settlement.

Written by the indexing model from the issue text.