Document the parameters for urllib3.request()

[alexwlchan]

This documents the urllib3.request() function, and a couple of its intermediaries, as described in #3011.

I built the docs locally to check the parameters were appearing correctly in both the user and reference guide. I did get one warning, but I think it was unrelated to my change. (urllib3/src/urllib3/contrib/socks.py:docstring of urllib3.contrib.socks.SOCKSConnection.socket_options:1:py:class reference target not found: connection._TYPE_SOCKET_OPTIONS)

https://urllib3.readthedocs.io/en/stable/reference/urllib3.request.html:

Before	After

https://urllib3.readthedocs.io/en/stable/reference/urllib3.poolmanager.html#urllib3.PoolManager.request (linked from request() in the user guide):

Before	After

Notes for reviewers

• Most of the parameter descriptions are copied directly from HTTP(S)ConnectionPool.urlopen(), with the exception of json and fields.
• I split the patch into individual commits as I was going along because I thought I might end up writing more detailed "where did this text come from" messages, but I can easily squash them down into a single commit if that's preferred.
• I didn't write a changelog entry because documenting a single function didn't feel like a change that needed one, but I can add one if you think it's important.

Fixes #3011

[illia-v]

Thanks!

I was concerned about exposing internal types on the provided screenshots, but the types look good like previously on https://urllib3--3177.org.readthedocs.build/en/3177/reference/urllib3.request.html

[sethmlarson]

LGTM too, thanks @alexwlchan!

[sethmlarson]

@alexwlchan This issue is eligible for a $100 bounty on our Open Collective! You can submit an expense there linking to this pull request and we'll review it :) Thanks again!