Do not delete entitiy fields in datastore when those entity keys are missing from the Entity model

[chaitanyanettem]

This becomes an issue when different Entity models are being used by different services to represent the same Entity. (It is a separate problem that the models shouldn't be different 🤔 but let's not go there).

For eg -

• In service A, the car Entity is defined as -

class Car(BaseModel):
    price: int = 5000

• In service B, the car Entity is defined as -

class Car(BaseModel):
    price: int = 10000
    brand: str = 'BMW'

if service A updates an entity which has the brand field, it should not remove the brand field.