Add additional Talk Notifications into Stream

[Bolli84]

Currently, only calls are logged into the activity-Stream or the mails.

Since Talk gains more and more speed, direct notifications in Chats should also be sent in the Stream/Mail-Notification.
e.g. @username-notification

The feature is like cloning in MS-Teams or others.
In the Nextcloud Talk app, it happens immediately, but users without Smartphone-connection do not get this. The activity stream could make it happen