[feature]: allow creating AMP invoices with blinded paths

[ZZiigguurraatt]

Would like to see this message to go away.

$ lncli addinvoice --amp --blind --amt 5
[lncli] rpc error: code = Unknown desc = AMP invoices with blinded paths are not yet supported
$

The idea of having an AMP invoice embedded inside a static BOLT11 invoice that can be re-used and with the privacy of a blinded path is promising. Seems like this would provide many benefits of BOLT12, without needing the onion messaging. Would be a lot less friction for industry adoption since LND and BOLT11 invoices are already well supported, just needing to change two flags in invoice generation and that is it.