fix: throw validation error when json is passed with invalid unstructured json

[jordan-homan]

Notes

Adds validation if json / ndjson are not valid unstructured schema.

Testing

Manually tested serverless API with example json:

test_length = [] = 200

test_invalid = [{"invalid": "schema"}] = 422
test_invalid_ndjson ={"hi": "there"} = 422

test_chunk = [{"type":"Header","element_id":"a23fdadef9277f217563e217ebd074d5" ... = 200