Move issuable sidebar below breadcrumb bar

What does this MR do and why?

Moves the issuable sidebar (on issues, epics, and incidents) below the fixed breadcrumb bar

Why?

• The issuable sidebar is a part of the issuable object, so it follows that its part of the actual issuable page layout. This is in contrast to the full-height global sidebar on the left
• This follows the pattern across other page layouts (the job page, the MR page, the issue board sidebar etc)
• Fixes some misalignments currently present on production

Alignment fix screenshots

:notifications_todos_buttons enabled

Before	After

:notifications_todos_buttons disabled

Before	After

Layout screenshots

:notifications_todos_buttons enabled

	Before	After
Issue
Epic
Incident

:notifications_todos_buttons disabled

	Before	After
Issue
Epic
Incident

How to set up and validate locally

• Enable :notifications_todos_buttons and check the following:

1. Issue: http://gdk.test:3000/flightjs/Flight/-/issues/1
2. Epic: http://gdk.test:3000/groups/flightjs/-/epics/1
3. Incident: http://gdk.test:3000/flightjs/Flight/-/issues/41

• Disable :notifications_todos_buttons and repeat

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 #430244 (closed), #424396 (closed)