Backend: Add ability to embed stack trace in gitlab issue

This goal of this issue is to

• Determine what technical approach we want to use to embed stack trace (GFM vs it's own separate section)
• Add the necessary backend such that a stack trace can be embeddable in a gitlab issue so that we can eventually embed the stack trace in a gitlab issue that was opened by the sentry error details page (#36545 (closed))

A gitlab issue should have a 1:1 relationship with a sentry issue for now based on a decision made in the team meeting.

Original design

Updated Design

To accommodate the fact that we need the stack trace to be a separate content block from the issue description, we propose the following:

• Stack trace would live above the related issue section
• The "headers" of each stack trace display as white rather than grey to fit better within the issue framework