Make issue/incident code more DRY

What does this MR do and why?

This MR improves issue/incident code to be more DRY

Screenshots or screen recordings

No visual changes

How to set up and validate locally

1. On an issue, check that
   1. the dropdown items in the ellipsis menu say issue
   2. there is a Linked items widget
2. On an incident, check that
   1. the dropdown items in the ellipsis menu say incident
   2. there is a Linked incidents or issues widget
   3. there are Summary, Metrics, and Timeline tabs

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.