[DOCS] Integration to FastAPI schema example can be updated to Pydantic v2

[danielMicallef]

Documentation for Integration with FastAPI example is still using Pydantic v1. FastAPI with Pydantic v2 support was released back in Aug 2023. Since Pydantic v2 introduces a number of API changes as discussed in the Pydantic migration guide, it would be ideal to reflect this in the documentation.

Specifically:

• orm_mode is deprecated and replaced by from_attributes. ref: https://docs.pydantic.dev/dev/migration/#changes-to-pydanticbasemodel
• validator is deprecated: ref: https://docs.pydantic.dev/dev/migration/#validator-and-root_validator-are-deprecated
  FastAPI with Pydantic v2 fastapi/fastapi#9709

Hence the Schema example can be updated from:

class CarOut(BaseModel):
    make: str
    model: str

class PersonInDB(BaseModel):
    name: str
    age: int
    cars: List[CarOut]

    @validator('cars', pre=True, allow_reuse=True)
    def pony_set_to_list(cls, values):
        return [v.to_dict() for v in values]

    class Config:
        orm_mode = True

to

from pydantic import BaseModel, field_validator


class CarOut(BaseModel):
    make: str
    model: str

class PersonInDB(BaseModel):
    name: str
    age: int
    cars: List[CarOut]

    @field_validator('cars', mode='before')
    @classmethod
    def pony_set_to_list(cls, values: list) -> list:
        return [CarOut.model_validate(v) if not isinstance(v, CarOut) else v for v in values]

    class Config:
        from_attributes = True