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

See merge request !7365