Leverage `orjson.dumps` as part of the native OBM json serializer

[butler54]

Issue description / feature objectives

Today most of the serialisation uses orjson, however, the native .json() method is still exposed. Use the json_dumps config attribute to change to orjson.

Following these: https://pydantic-docs.helpmanual.io/usage/exporting_models/#custom-json-deserialisation instructions worked, however, orjson options (such as indenting) could not be passed.

Caveats / Assumptions

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