Fully Implement NWC HOLD invoices spec

See https://github.com/nostr-protocol/nips/pull/1913

at least `min_cltv_expiry_delta` is missing. For LDK we need to make a minor change in our fork to allow passing that. For LND it should be immediately possible.

- [x] LND  #2139 
- [ ] LDK https://github.com/getAlby/ldk-node/issues/92