Location button shows when source code URL is empty

[rossturk]

When there is no source URL for a job, the web UI still shows a button that doesn't link anywhere.

Perhaps the button should not show up of there is no source code location? Better still, it could be disabled with a tooltip explaining how the connection can be made w/a link to some docs.

I believe the work happens here: https://github.com/MarquezProject/marquez/blob/e5c1fea533b11fd42d25b8efe5125757d0cd2914/web/src/components/jobs/JobDetailPage.tsx#L89