Display unread messages
Description
The new Chat component vue-advance-chat can also display which messages are unread.
At the moment the foodsharing backend stores only that there are unread messages for a conversation.
Impact
Proposal
- Implement unread messages in the backend
- Set the
seen
attribute in https://gitlab.com/foodsharing-dev/foodsharing/-/blob/nini1988-refactor-chat/client/src/views/pages/Message/ChatComponent.vue#L303