Add hint in notification for file share with caption

[DorraJaouad]

Describe the solution you'd like It would be nice to know that it is a file share with caption from the notification, rather then just seeing the caption as a normal message.

Describe alternatives you've considered Could be an emoji of a picture or a file , or maybe a small preview of the image.

[SystemKeeper]

When we are able to get a preview, it should also be visible, see https://github.com/nextcloud/talk-ios/pull/1306 But that sometimes fails server side :(

boils down to https://github.com/nextcloud/talk-ios/pull/963