doc(notification): add in-app notification docs#9824

rafaeltonholo wants to merge 1 commit intothunderbird:mainthunderbird/thunderbird-android:mainfrom

rafaeltonholo:docs/9252/document-new-notification-system-apirafaeltonholo/thunderbird-android:docs/9252/document-new-notification-system-apiCopy head branch name to clipboard