Block API users

[michielp1807]

Closes #349

TODO:

• Block users in backend
• Add unit tests for blocked accounts
• Update admin interface to allow blocking accounts
• The admin interface can now also be used to delete API users (closes Delete ApiUser from admin interface #117)
• Fix playwright tests for admin interface
• Consider adding a "full freeze" block status to organizations

[codecov]

Codecov Report

❌ Patch coverage is 89.47368% with 12 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/api/oauth/handlers.rs	0.00%	5 Missing ⚠️
src/models/api_user.rs	89.18%	4 Missing ⚠️
src/api/api_users.rs	90.90%	2 Missing ⚠️
src/api/auth.rs	96.96%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[squell]

I've given the front-end code a more lax review (based on clicking around in staging).