Create setting/flag to enable/disable X-Forwarded-Port

[victor-torres]

Summary

Create a new setting/flag to enable/disable X-Forwarded-Port to populate remote address info.

This flag is disabled by default. Command line options are:

• --forwarded-port
• --no-forwarded-port

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

[victor-torres]

This pull request is addressing the issue described in #1974

[victor-torres]

There's a failing test case in tests/supervisors/test_multiprocess.py that I don't think is related to this PR.
It fails on Python 3.9 running on macOS.

I think this PR is ready for review. Let me know if I can help with anything else or if there's anything that could be improved here :D

[Kludex]

Do we need to add a new flag?

[victor-torres]

I don't mind considering X-Forwarded-Port (if available) by default if already checking for X-Forwarded-For.

My decision to include a new flag was to avoid changing the default behaviour, something that some maintainers and some users usually ask for.

But I can totally remove the flag and make it be considered by default +1

Just let me know.

[Kludex]

Let's take a step back here, and continue the discussion on #1974 (comment), please.

[Kludex]

I'll be closing this until we have a decision on the issue.

I don't think we want this to be a parameter anyway.