Kiwitcms-github-app

- Update for newer PyGithub

- Adjusted to work with Django 3.1 and Kiwi TCMS > 8.6
- Replace deprecated ``url()`` with ``re_path()``
- Migrate the ``payload`` field to newer ``models.JSONField`` type
- Setting ``PUBLIC_VIEWS`` is removed in Kiwi TCMS so remove the
automatic adjustment
- Make error messages for missing AppInst more clear
- Remove redundant if condition in Resync()
- Update translation strings
- Update documentation around GitHub permission requirements for
1-click bug report

- Add GitHub issue-tracker integration which authenticates as the installed app. Fixes Issue 25
- Configure BugSystem for new repos. Fixes Issue 15
- Create Product & BugSystem records when installation_repositores change. Fixes Issue 21
- Trigger resync from GitHub via menu. Fixes Issue 19
- Trigger resync from GitHub after AppInstallation is configured. Fixes Issue 20
- Database: Add AppInstallation.settings_url field
- Link to the correct URL for GitHub settings. Fixes Issue 33
- Require user to be logged in for ApplicationEdit. Fixes Issue 36
- Update translation strings
- Add more tests

- Install settings overrides under ``tcms_settings_dir/``
(compatible with Kiwi TCMS v8.2 or later):

- does not need ``MIDDLEWARE`` and ``PUBLIC_VIEWS`` override anymore
- Remove ``GithubAppAuth`` backend, shipped with social-auth-core v3.3.0
- Fix a redirect to use the correct name of our social_core backend

- Do not fail if product already exists
- Do not fail if repository doesn't have description
- Search UserSocialAuth by uid and provider

- Address GitHub API deprecation not yet fixed in social-auth-core