Abstract NUT-17 subscription kinds to their respective NUTs

[gudnuf]

As new NUTs are added we may want to extend the supported websocket subscription kinds. Right now, NUT-17 defines "bolt11_mint_quote", "bolt11_melt_quote", and "proof_state".

Based on this discussion I would propose that we do not define the specific subscription kinds in NUT-17. We should instead abstract NUT-17 and define the bolt11 kinds in NUT-23 and the "proof_state" kind in NUT-07. Then we can define bolt12 specific kinds for #259

[thesimplekid]

I agree, would you be interested in opening a PR for this?

[gudnuf]

I agree, would you be interested in opening a PR for this?

Yea sure, I will do later today