`generateLSP4MetadataJSON` function

[YamenMerhi]

We should add generateLSP4MetadataJSON function to generate the JSON from the available fields.
We could add several overloads

[YamenMerhi]

Probably we can add generateLSP4MetadataUtf8

[richtera]

That's not really necessary I think. The hash is identical unless you pretty print. And if you pretty print we support that one as a backup in erc725.js