Redirect previous incident route to issue route

What does this MR do and why?

Describe in detail what your merge request does and why.

When receiving an incident route on an Issue that no longer has a type of Incident, reroute to Issue route instead of showing a 404.

Further description from this comment from @syasonik

Drive-by explanation: Let's say I have an incident, and I've shared a link to the metrics tab of the incident (format like /project/-/issues/incident/355/metrics).

BUT then, I change the issue type of the incident to a standard issue. So that issue still exists, but the url doesn't make a ton of sense anymore, since standard issues don't have a metrics tab.

Redirecting to the issue path lets us handle that scenario gracefully for the user, so the url still resolves.

This MR is based on !108950 (merged), which is turn is based on !112342 (merged). They both must be merged before this is merged, when this is merged it should be merged to master

Screenshots or screen recordings

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How to set up and validate locally

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

1. Open an issue that is type of issue, not incident
2. Add /timeline to end of URL
3. Expected behaviour is for /timeline to be striped from URL

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.