[Python] Add Python wrapper for JsonExtensionType

[rok]

Describe the enhancement requested

We added JsonExtensionType and we should make it usable from Python.

Component(s)

Python

[raulcd]

should this be a release blocker? @jorisvandenbossche @rok

[rok]

It's a nice to have for me, as it matches duckdb adding it. duckdb/duckdb#13446

[raulcd]

I am really close to create RC0. I don't think we should block the release for this. I'll move this to 19.0.0 once I create RC0

[rok]

Please go ahead.