feat: introduce middleware classes

[JasperSui]

Description

Since we can't process the request and response produced by django rest framework in an intuitive way currently,
so I try to introduce the middleware classes to django rest framework discussed in #7770.

If we can have the middleware classes for django rest framework only, then we don't have to implement the django middleware. The most important thing is we can process the request and response in django rest framework just like how middleware mechanism works in django, but without coupling the context between django and django rest freamwork.

[JasperSui]

@auvipy I don't know how to fix the CI for Python 3.9, and I've seen this happened in other opened PRs too, I'll be happy to fix that if you can help me figure that out, thanks!

[auvipy]

what about extending django middleware mechanism instead?

[JasperSui]

You mean the whole flow of django middleware or just subclassing the django.utils.deprecation.MiddlewareMixin?

[auvipy]

DRF is an extension to django so we should be able to write custom middleware for DRF using django base middleware mechanism and custom it aligning with DRF's flow of reqquest response

[lovelydinosaur]

Appreciate the input, tho... https://github.com/encode/django-rest-framework/blob/master/CONTRIBUTING.md

At this point in its lifespan we consider Django REST framework to be essentially feature-complete. We may accept pull requests that track the continued development of Django versions, but would prefer not to accept new features or code formatting changes.