Add more attributes to work items list page

What does this MR do and why?

Add more attributes to work items list page: the milestone, due date, weight, and health status is now shown.

No changelog required as it is behind the feature flag namespace_level_work_items

Issue: #392812 (closed)

Subsequent MRs will filter the work items into open/closed/all tabs, add searching, add filtering, add sorting, etc.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. In rails console enable the FF

   Feature.enable(:namespace_level_work_items)

2. Go to an issue (e.g. http://127.0.0.1:3000/flightjs/flight/-/issues/1) then create a new task in the Tasks widget
3. Click on the new task and add various attributes like milestone
4. Visit the group work items page such as http://127.0.0.1:3000/groups/flightjs/-/work_items
5. Check that the basic UI is there

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.