Add filters to work items list

What does this MR do and why?

Add filters to work items list (#457009 (closed))

Adds confidential, group, and my-reaction filters

Behind feature flags

• work_item_epics
• work_item_epics_rollout
• namespace_level_work_items

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screen_Recording_2024-07-18_at_6.26.21_PM

How to set up and validate locally

1. In rails console

   Feature.enable(:work_item_epics)
   Feature.enable(:work_item_epics_rollout)
   Feature.enable(:namespace_level_work_items)

2. Visit any work items list page for a group such as http://127.0.0.1:3000/groups/flightjs/-/work_items
3. Test the search bar filters

Related to #457009 (closed)