Close feature spec gap for work items and OKRs

Shortly before the release of OKRs we found a few bugs that made it into production but could have been prevented by feature specs. Examples of recent bugs:

• !108581 (merged) (would have been caught by a feature spec)
• !107246 (merged) (would not have been caught by a happy-path feature spec, but a feature spec could prevent feature regression)
• !107360 (merged) (unfortunately would not have been caught by a feature spec, but was not a visible bug)
• !109002 (merged) (could have been caught, but we'd have likely not implemented it as a feature spec. Maybe as a regression)

This issue is about closing the gap of the feature specs for the features we have so far.

Another reason why this is important: Work Items code will be at some point drive even more features in the future (Epics, Issues, Tasks, OKRs and KRs). We therefore need the same confidence for changes as we have right now for Issues and Epics.