Add `index` field to schema on the fly

[korenmiklos]

This is a UX issue: the user should not care about how we index rows.

class EducationItem(BaseModel):
    index: int
    year: Optional[List[str]]
    university: Optional[List[str]]

should become

class EducationItem(BaseModel):
    year: Optional[List[str]]
    university: Optional[List[str]]

and the code should modify the model.