Add django-mongodb-backend support

[aclark4life]

Hello! I'm working on 3rd party library integration for Django MongoDB Backend e.g.

• Replace hardcoded pks in tests carltongibson/django-filter#1703

Description

This draft PR adds an ObjectIdRestField to DRF for use with Django MongoDB Backend. With this PR, many DRF test suite errors change from expected int, got ObjectId to errors like:

___________________________________________________________________________ SearchFilterTests.test_search_field_with_custom_lookup ____________________________________________________________________________
tests/test_filters.py:225: in test_search_field_with_custom_lookup
    assert response.data == [
E   AssertionError: assert [{'id': '67be...text': 'abc'}] == [{'id': 1, 't...'title': 'z'}]
E     
E     At index 0 diff: {'id': '67be0f743ca9f525d672ebcc', 'title': 'z', 'text': 'abc'} != {'id': 1, 'title': 'z'
E     
E     ...Full output truncated (2 lines hidden), use '-vv' to show

Many of these errors can be fixed by removing hard coded pks similar to carltongibson/django-filter#1703.

Planning to remove hard coded pks in a future commit after which I'll remove draft status. Any and all feedback appreciated!

[auvipy]

this PR is out of the scope of this project. I suggest you send a PR to drf-extensions

[aclark4life]

Thank you! I will check out https://github.com/chibisov/drf-extensions

[aclark4life]

@auvipy Actually, now that I think about it, there is nothing MongoDB specific in here … we're interested in updating the test suites of various 3rd party libraries so that both int and ObjectID pks can pass. E.g.

• Replace hardcoded pks in tests carltongibson/django-filter#1703

Please consider having another look! Thank you 😄