Tidy issue/incident code

What does this MR do and why?

This MR tidies issue/incident code and removes some duplicate code.

No changelog as there are no user changes

Screenshots or screen recordings

How to set up and validate locally

Checking issues

1. Go to issue http://127.0.0.1:3000/flightjs/Flight/-/issues/1
2. Confirm there are no error messages, confirm the top button says Close issue and the ellipsis dropdown menu contains New related issue and Delete issue
3. Click Close issue > confirm there are no error messages

Checking incidents

1. Go to http://127.0.0.1:3000/flightjs/Flight/-/incidents > Click Create incident
2. Add title > Click Create issue
3. Confirm there are no error messages, confirm the top button says Close incident and the ellipsis dropdown menu contains New related incident and Delete incident
4. Click Close incident > confirm there are no error messages

Checking hasClosingMergeRequest change

1. Go to http://127.0.0.1:3000/flightjs/Flight/-/merge_requests > Click New merge request
2. Click Select source branch dropdown > select any branch > click Compare branches and continue
3. Add Closes #1 to description > click Create merge request
4. Go to issue #1 http://127.0.0.1:3000/flightjs/Flight/-/issues/1 > Scroll down to Related merge requests widget and confirm it says When this merge request is accepted, this issue will be closed automatically

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.