Correct link to technical interview and re-arrange Developer page

I was making edits to the security specialist role, when I noticed broken link to the technical interview. One thing led to another, and now we have this merge request.

I'm a bit confused about careers vs jobs vs positions, and also in this case I opted to keep the technical interview on the careers page, but perhaps it should be kept on hiring/interviewing/technical after all. In any case it's all not terribly DRY right now. @chloemw @sashab @brittanyr what's the direction?

\cc @DouweM