Add grammar for BOLT12

[tee8z]

This should make it possible to send BOLT 12 invoices through different implementations. It is okay if the PR does not add support for LND as that implementation requires LNDK to be running along side of it which is a much bigger change required. However, if someone has the inclination to tackle both adding LNDK plus all the other implementations bolt12 for the grammar it would be appreciated. To start, take a look at SEND_LN command and see if there would be a good way to signify bolt12 maybe like how we do for amp or keysend at the moment. Any addition needs to be backwards compatible with the grammar already created so run through the many example script with the new grammar to verify everything works as expected.