Add documentation about how to transform factory request to DRF request

[mgaligniana]

Description

Hi there!

As there were many issues opened around this topic: "APIRequestFactory does not return a Request object" I think it would be worth to have a place in the documentation where explains it.

Following the Tom's comment in the last issue #6488 (comment):

If someone's invested and there's clearly a good existing place in the docs to highlight this, then we could accept a docs PR here.

*Past issues related: #4440 and #3608

This is what my proposal looks like:

I've also added a test to follow the Carlton's comment #6488 (comment)

Thank you!

[mgaligniana]

Hi @carltongibson! Is something like that the documentation you had in mind?

[carltongibson]

Hi @mgaligniana, it's similar!

I think people do this when they're testing individual view methods, without going via dispatch.

So, I'd be inclined to say, and show, that. I.e. what you have plus initial() and calling a (fictional) view method, which would be the point of the test.

Make sense?

But, yes, great.