Provide intersphinx objects.inv

[mschoettle]

I started using mkdocs with mkdocstrings [1] and it has the ability to import objects.inv (see intersphinx) files to reference elements from other projects. Unfortunately, DRF does not provide this file.

I am aware that you are using mkdocs and the aforementioned mkdocstrings actually generates the objects.inv file. So I am wondering whether there is interest to provide this. It would be great to be able to reference a code element in docstrings and have it link automatically to the relevant part in the DRF documentation.

[1] https://mkdocstrings.github.io/

[onegreyonewhite]

@mschoettle here is #9587