Render 404 when Jira issue not found

What does this MR do and why?

This renders a 404 error page when a Jira issue cannot be found instead of a 500 error.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Create a project
2. Go to `http://localhost:3000/{PROJECT_PATH}/-/settings/integrations/jira/edit
3. Enter Jira credentials (I have a Jira test namespace and can share the credentials. Ping me on Slack)
4. Make sure to check Enable Jira issues and enter the Jira project key
5. Visit http://localst:3000/{PROJECT_PATH}/-/integrations/jira/issues/UNKNOWN-99999
6. Observe a 404 page instead of 500 error.

MR acceptance checklist

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