Job Editor UI: `job-editor.hbs` has `mode="javascript"` instead of `ruby`

For, for example job templates, leads to a worse experience with syntax highlighting

(we probably want `mode` to be a passed value, as there are time where it's appropriate to be javascript, for example job definition route)

Start in job-editor.hbs and inspect how the editor is used for job templates and the job definition route. Confirm which contexts need Ruby or JavaScript highlighting, then verify that the template editor uses the appropriate mode without changing the route that requires JavaScript.

Written by the indexing model from the issue text.