bpo-47126: Update to canonical PEP URLs

[hugovk]

With the recent implementation of PEP 676 the canonical URL for PEPs has changed from, for example:

https://www.python.org/dev/peps/pep-0008/

to:

https://peps.python.org/pep-0008/

Redirects are in place so the old links still work, but let's update the docs and docstrings to use the new canonical form. There's also a couple of places in code.

Also removed r'http://www.python.org/dev/peps/pep-\d+' from the docs linkcheck. There are no URLs of that form in main, they're all https, so this isn't needed.

Also updated RFC link generator to use https instead of http, because it was right next to the PEP link generator being changed. I can drop this change if necessary.

https://bugs.python.org/issue47126

[hugovk]

Updated to bump Sphinx to 4.5.0 which updates the :pep: role to use the new canonical URL form.

• https://www.sphinx-doc.org/en/master/changes.html#release-4-5-0-released-mar-28-2022
• environment: Update default value for pep_base_url sphinx-doc/sphinx#10267
• Update to canonical PEP URLs devguide#822

[pablogsal]

LGTM

[pablogsal]

Great work @hugovk 🎉