[#1635]Add model name in DoesNotExist and MultipleObjectsReturned message

[BraveEggTart]

Description

Add the model.name field to the DoesNotExist and MultipleObjectsReturned exception message to obtain clearer prompts when calling the model. get() method.

Motivation and Context

When I use the Model.get() method and a DoesNotExist exception occurs because there is no corresponding record in the database, the provided error message is often not specific enough for me to quickly identify which Model is involved. The message "Object does not exist" is too generic.

#1635

How Has This Been Tested?

I executed the make test command and passed all tests related to the get() method, such as the test_get method in test_queryset.py.

testing environment: python: 3.10.6

There's something I need to say. I checked the code about DoesNotExist and MultipleObjectsReturned, and noticed that in the _getbypk method of models.py, DoesNotExist was processed and returned cls._meta.full_name, Is this a place that needs to be modified synchronously?

    @classmethod
    async def _getbypk(cls: Type[MODEL], key: Any) -> MODEL:
        try:
            return await cls.get(pk=key)
        except (DoesNotExist, ValueError):
            raise KeyError(f"{cls._meta.full_name} has no object {repr(key)}")

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[abondar]

Hi!

Sorry for confusion - just merged #742 which did basically the same few hours before
Still hope your problem is resolved by merged change, I will release it as 0.21.4 a little bit later