Get more alpha users of Snowflake to stress-test before stable

In a discussion before the stable release of Tor Browser 9.5, we discussed that we'd like to get more snowflake users before moving it out of alpha so that we can stress-test the system to make sure it will work with the massive increase of users we get in stable.

This ticket is to track that progress and perform measurements. We have tpo/applications/tor-browser#40027 (closed) open as a way to get more alpha testers on mobile.