Convert issueId and issueIid to string in issue app

What does this MR do and why?

This MR converts issueId and issueIid to strings as suggested in an MR review #427178 (closed)

It also deletes some dead code

Screenshots or screen recordings

No visual changes

How to set up and validate locally

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 #427178 (closed)