Issues: consolidate buttons

What does this MR do and why?

This MR consolidates buttons in the issues header region. It moves the edit button to the issue header. This change aligns with recent changes for MRs.

Screenshots or screen recordings

Issues

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Incident

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Epics

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For comparison: MRs

MR edit	MR close

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

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