Cross reference documentation with mkdocstrings' `objects.inv`

[Raventric]

Discussed in #3091

Well I say discussed but in reality it got no response so i'm trying to follow up. Does httpx provide objects.inv for documentation cross-reference? mkdocstrings generates this automatically unless explicitly disabled and it allows for third party packages relying on httpx to better document their projects and easily refer to httpx's documentation.

https://mkdocstrings.github.io/usage/#cross-references-to-other-projects-inventories

[Tom Christie]

Hey @Ravencentric - thanks for the prompt.
Have responded on the discussion as a starting point.

(Closing the issue for the moment, but up for the discussion and reopening if we get to a clear resolution.)