feature request: support extensible data fields

I would like to add support for extensible data to this implementation of the IPNS record.

This could be done by:

adding an optional extensibleData field to CreateOptions.
adding an optional parameter extensibleData to createCborData.
inside of createCborData, merge extensibleData the data object.
add tests and documentation

It's not necessary to change types or add generics to the record type. Users of this feature would simply have to decode IPNSRecord.data to read any extensible fields.

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Thank you for posting this issue, I had the exact same question, and you saved me the time reading through the docs

Oh look what I found,

js-ipns/src/index.ts

Line 65 in f622fc8

* extensible data

It's just waiting for a pull request

@tabcat I got a working POC of extendable for js-ipns in this pull requres

#309

@tabcat if you want to use it check my tests, https://github.com/dentropy/js-ipns/blob/main/test/extensible_data.spec.ts

You have to recast js-ipns type IPNSRecordData as any to get the data out