Revise and clean up Jira issues page
Reviews the changes made in !55773 (diffs) (which were included in the big Jira split-apart work in #324250 (closed)).
This information is now in doc/integration/jira/issues.md - this page needs a CTRT cleanup anyway, so let's handle two issues at once. Assigning @cnorris for a tone/style review and @deuley for a content review.
Related issues
- Closes #323622 (closed)
- Related to #327784 (closed) where I've agreed to clean up multiple pages.