Use Pydantic for json serialization in .to_json method

[EspenHa]

This PR changes the to_json method of generated models to use
Pydantic's to_jsonable_python, to ensure that the input to json.dumps only contains serializable types.
This fixes #22063.

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[EspenHa]

Tests seem to be failing due to differences in how json is generated in Python's stdlib json module, and pydantic.

I might come back and fix this later if there is interest for moving this PR forward.

[wing328]

@EspenHa thanks for the PR

can you please PM me via Slack to discuss this further?

[EspenHa]

@wing328 I added tests for serializing UUIDs. This PR should be ready to merge.

[iFurySt]

We're facing an issue with datetime fields causing JSON serialization failures. This PR should fix both UUID and datetime serialization. Do we plan to merge this PR soon? @wing328 :)

[wing328]

merged via #23210 with update samples and all tests passed