Resolve "Implement issue preview in a drawer on issue list page"

What does this MR do and why?

This MR implements an issuable drawer on the project issues list page. Instead of being redirected to a standalone page, on clicking an issue link user sees an drawer open, and they can modify issuable properties, delete an issuable, change issuable state etc. All these changes are reflected in the list. For more details, please see a video recording below.

Screenshots or screen recordings

Drawer_demo

How to set up and validate locally

1. In rails console enable the issues list drawer feature flag

   Feature.enable(:issues_list_drawer)

2. Open any project -> issues list
3. Click on the issue. You should see the drawer open on the right side.
4. Try to edit issuable properties in the drawer. This should update them in the issues list.

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 #414784 (closed)