feat(settings): Add CAD button in Connected Services when signed into Fx Desktop
Because: * We want a more persistent 'pair' button near connected services in Settings. The current CaD promo can be dismissed This commit: * Adds this button, and is displayed under (mostly) the same condition as the promo banner - Firefox Desktop. Leaves the case for the promo banner for if the user is signed in to Firefox. closes FXA-13797