Render WorkItemLinks widget in issue page

What does this MR do and why?

Render the work item links widget in the current issue view.

Screenshots or screen recordings

How to set up and validate locally

1. Enable feature flags:

Feature.enable :work_items
Feature.enable :work_items_hierarchy

2. Navigate to issue page and see the Child items widget.

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.

Related to #362860 (closed)