This is a backport of PR #3679 as merged into main (2e0c293).

Quicker alternative to #3653 for fixing #3639

I must add that this is not the "correct way" of fixing it, but its quick and safe (in the sense that it leaves us in a similar state we had before, where all jsonfields were recognized as Objects). Its not the correct way because:

• the schema type is misleading, which is not helpful for users. E.g, its says its an Object (openapi type) when its an Array example
• its not doing basic structural validation (often we know exactly what the json structure is)

Reference

• Relevant drf-spectacular docs:
  • https://drf-spectacular.readthedocs.io/en/latest/customization.html#step-3-extend-schema-field-and-type-hints