Together with #415 this finally adds the field flag to all entity listings.
closes #342
### ⚠️ breaking changes ⚠️
This changes the column names of `tea milestones ls`:
```diff
- TITLE | OPEN/CLOSED ISSUES | DUEDATE
+ TITLE | ITEMS | DUEDATE
```
Co-authored-by: Norwin <git@nroo.de>
Co-authored-by: 6543 <6543@obermui.de>
Reviewed-on: https://gitea.com/gitea/tea/pulls/422
Reviewed-by: delvh <dev.lh@web.de>
Reviewed-by: 6543 <6543@obermui.de>
Co-authored-by: Norwin <noerw@noreply.gitea.io>
Co-committed-by: Norwin <noerw@noreply.gitea.io>