Add dividers between items within the work item lists

What does this MR do and why?

This MR

• adds $gray-50 border between Child items and Linked items
• Include 4px spacing between items and the divider
• On the Linked items widget, remove the borders between relationship types (Blocked, Blocking, etc)
  • Instead of borders, increase the spacing between these sections to 24px
• Remove the glitch of expand button when more records are fetched using Load more button
• Align remove button which were regressed due to introduction of crud component

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.

	Before	After
Child items border
Child item's children with border
Child items border with paginated data
Linked items border
Expand button on Load more action	Screen Recording 2024-08-30 at 9.30.27 PM.mov	Screen Recording 2024-08-30 at 9.28.06 PM.mov
Align remove button

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Prerequisites:

1. Enable the OKRs feature as mentioned in the OKRs docs (e.g. ::Feature.enabled?(:okrs_mvc, Project.find(<PROJECT_ID>)) and the namespace must have Ultimate plan).
2. Enable Epic work items
   1. Feature.enable(:work_item_epics_rollout)
   2. Feature.enable(:work_item_epics)

Steps to verify at Group level:

1. Login with any user
2. Go to Group > Epics
3. Open or create an Epic
4. Create or add existing child items
5. Verify if borders are appearing between items and its child items
6. Link few items in Linked items widget
7. Verify if the borders are applying properly

Related to #479187 (closed)