Ln verification do not use payment_hash as verification identifier

[86667]

Create a new Id uuid on ln verifications instead of using payment_hash.

Also adds ln_verificaiton/price endpoint to fetch configured invoice price.

Breaking change

This db schema change is breaking in Staging. (Production is not yet deployed)
I'll manually drop the tables before depploying:

DROP TABLE IF EXISTS lightning_verifications;
DELETE FROM migrations WHERE name = 'm20251216_create_ln_verification';

[SeverinAlexB]

Let's go. Code looks flawless 🚀