Update Milestone Report page

What does this MR do and why?

Updates Milestone Report page to include epics and show UI updates

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

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Page Before	Page After

How to set up and validate locally

Make sure you have work_items_alpha feature flag enabled. To add a milestone to an epic, you need to create a group level milestone and also have work_item_epics_ssot FF enabled.

Go over the page and check off the UI updates listed in the issue's description: #519589 (closed)

Or you can also compare to the design: #425088[Mileston_Report.png]

Toggle work_items_alpha on and off to see the difference in UI.

Related to #519589 (closed)