Markdown rendering support for new "New issue message" (BB-11327)

New issue message on issue tracker settings has a WYSIWYG editor but the message is rendered out as plain text (read: markdown is not processed)

How to reproduce

1. Go to the repo's issue tracker settings
2. Enter a markdown message in the New issue message editor.
3. Save
4. Create a new issue on the same repo

Actual result

The message is rendered in plain text.

Expected result

The message should be processed by markdown and be rendered with the appropriate HTML.

If the message is not intended to be markdown enabled, then shouldn't the editor be just a textarea instead of a WYSIWYG?