Customizable conversion to/from bytes for schema registry JSON serde

[sabnatarajan]

I’d like to suggest a feature for the schema registry JSON serializer/deserializers to make the conversion from dictionary to bytes (and vice-versa) customizable. I thought this could be done using a callable similar to the to_dict / from_dict argument. This would be useful for those who might want to use a different JSON library (like orjson) or implement custom serialization logic.

If this sounds like something that would be well-suited for the library, I’d be happy to contribute! Let me know your thoughts or if there are any specific considerations I should keep in mind.