Merge sidebar and work item Apollo client instances

What does this MR do and why?

This MR aims to create the common shared Apollo cache for sidebar widgets and work item hierarchy on the Issue page. This allows us to remove an event hub as a communication tool as now both applications have access to the issue state via Apollo cache.

Screenshots or screen recordings

No visual changes

How to set up and validate locally

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

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 issue: #370753 (closed)