Add a tag to zap receipt

[benthecarman]

Wanted to update to lastest version of rust-nostr to do this but in that release they changed kind numbers to be stored in u16s which is not compatible with the ones we use for registration in here. Instead of waiting for another release of rust-nostr we can just manually create the zap receipt ourselves, this is just a copy-paste of the rust-nostr version that we use EventBuilder::zap_receipt but adds the a tag if available.

This will fix the issues people had with using our lightning address with zap.stream