Add code_challenge_methods_supported property to OIDC auto discovery

[gutard]

Fixes #1249

Description of the Change

Some OIDC clients require code_challenge_methods_supported to be present in auto discovery information. The PR adds this property to ConnectDiscoveryInfoView.

Checklist

• [x] PR only contains one change (considered splitting up PR)
• [x] unit-test added
• [ ] documentation updated
• [x] CHANGELOG.md updated (only for user relevant changes)
• [x] author name in AUTHORS

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (2d641f2) 97.54% compared to head (3ac4115) 97.54%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1367 +/- ## ======================================= Coverage 97.54% 97.54% ======================================= Files 32 32 Lines 2120 2120 ======================================= Hits 2068 2068 Misses 52 52 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[gutard]

Also please "Make sure to request a review by assigning Reviewer jazzband/django-oauth-toolkit" when you are ready for review.

Yes I read this but I think I'm not allowed to. From GitHub docs:

Note: Pull request authors can't request reviews unless they are either a repository owner or collaborator with write access to the repository.