[Onboarding] Improve retention users ("net growth" user) by Sending notifications during User Onboarding

[astronault]

WHY

20% to 50% of a user cohort uninstall tabby because "tabby doesn't work" / "did not work" / "not working etc.
It seems they only have a few tabs when they install tabby, so indeed, they don't see tabby working... but there could be other reasons. Also, our current onboarding videos don't seem to work (# of views on YouTube), people might skip them. So we need to think about a more efficient and simple onboarding.
-> The bigger the cohorts, the more important it will be to improve our retention metrics: the "net user growth" will increase and this is a huge-win

WHAT

I suggest we insert an onboarding notification when sby downloads tabby.
This notification needs to prove that tabby is aware of the number of tabs, so it could say :
"Hey! You currently have 7 tabs open. Open the settings, and switch to "focus" mode to see tabby working. Change settings anytime."
(customization)
If people have currently_number_of_open_tabs > 15 tabs, subsitute "focus" mode with "relax" mode.

-> it should be smooth enough to just SHOW that tabby works, without tabby to destroy the current working setup of the user