First load experience for guest user

[jaril]

Moved from 4859.

https://www.loom.com/share/fdf1039deca24a9e80dfb8d78994fd6d

The main points appear to be:

• the user is not told what replay is in the first place, or what they're looking at.
• sign in is confusing (for reasons documented in https://github.com/RecordReplay/devtools/issues/5065)
• loading screen should differentiate between logged in/not.
• Replay Info, is it important?

[jonbell-lot23]

March 15, 2022:

This seems like the sort of thing I can take on, especially as part of the onboarding audit.