Problem: Need ability for admin to modify dynamic settings

[julianpistorius]

In particular for the 'enforcement override' functionality.

Currently one has to modify the config file and restart services.

Solution: Add the 'Constance' Django plugin and modify logic which
currently uses static settings.

See: https://github.com/jazzband/django-constance

Checklist before merging Pull Requests

• New test(s) included to reproduce the bug/verify the feature
• Add an entry in the changelog
• Documentation created/updated (include links)
• If creating/modifying DB models which will contain secrets or sensitive information, PR to clank updating sanitation queries in roles/sanitary-sql-access/templates/sanitize-dump.sh.j2
• Reviewed and approved by at least one other contributor.
• New variables supported in Clank
• New variables committed to secrets repos

[julianpistorius]

Predictably (fortunately) the tests failed.