Review "Become an Alpha Tester" page content and workflow

For P163, we have a new goal of recruiting new alpha testers.

We should take this opportunity to review the content on this page based on previous interactions. https://community.torproject.org/user-research/become-tester/

For example, who's the role of granting "Alpha tester" badge? https://forum.torproject.org/badges/104/alpha-tester

cc @bella, @donuts, @morgan, @ebanam