Feat: make taskprocessing task types toggleable

[janepie]

• Resolves Toggle task types in admin settings assistant#157

Summary

Makes taskprocessing task types toggable in AI admin settings: disabled types will not be available and will not show up in e.g. the assistant.
Task types are enabled by default. The values are stored in a new appconfig db record.

Before:

After:

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required feat: describe task type disabling documentation#12424
• Backports requested where applicable (ex: critical bugfixes) not applicable