Decouple account management from settings sync

[aeschli]

Testing #93811

By playing around with the new account management feature I logged in to two Microsoft accounts and a Github account:

This looks really cool! So the idea is that this becomes a centralized place for managing the accounts I'm signed-in, correct? '

Settings sync would just one client of this, using one of the accounts. However, currently, settings sync seems to be more than just a regular client

• it pops up automatically when I logged in to a new account and ask to start settings sync. It shouldn't do that, maybe I just add an account for some other purpose.
• when I stop settings sync, it logs out from the account. It should prompt me before doing that. Maybe I want stay logged in for another feature.
• when turning on settings sync, it only proposes one of the accounts I've been logged in
  
  I would expect to also see my other account there. 'Use another account' brings me to a Microsoft web page like when creating a new account.

Feel free to close the issue if I misinterpreted the feature.

[sandy081]

/duplicate

#94766