Bring back the old JIRA docs

What does this MR do?

Bring back the old JIRA docs

Why was this MR needed?

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6598 introduced new JIRA settings, but that's not yet released. Since our documentation is currently built using the master branch, users are having issues where the docs show different settings than what GitLab's latest stable release supports.

What are the relevant issue numbers?

https://gitlab.zendesk.com/agent/tickets/48003