WIP: Make Brotli support enabled by default, if appropriate urllib3 version is available

[gdubicki]

This is still a work in progress - I have to make sure that the tests are actually running, not skipped every time 😅 but I would like to get feedback if the direction is right.

I had to update some deps to make the tests pass after a lot of packages being updated after I added brotli to dev-packages. But I assume that this should be done anyway. Especially as there were discrepancies in the versions - f.e. pytest version in setup.py commit message declared v. 4 compatibility while the version in Pipenv was set to be at most v. 3.10.1.

Speaking of dependencies I have a doubt how to declare required urllib3 version. Technically the first with brotli support is 1.25.1, but this is a version not supported by Requests... Should I update all the references to require urllib3 >= 1.25.2 then instead of >= 1.25.1?

[gdubicki]

Ping! :)

[sethmlarson]

FYI Requests already supports Brotli via urllib3:

import requests

http = requests.Session()
http.headers = {"Accept-Encoding": "br"}

resp = http.request("GET", "https://cloudflare.com")
print(resp.text)
print("Content-Encoding:", resp.headers["Content-Encoding"])

[gdubicki]

@sethmlarson : yes, I know. Please see the updated PR title. I hope my intent is more clear now. :)

[dilyanpalauzov]

At #5783 I took a different approach: rely on urllib3 to determine whether to include ,br in the Accept-Encoding header.

[gdubicki]

Closing in favor of #5783.