Allow to re-leave the group if we are not part of the group but keep receiving messages

If we keep receiving messages in the group we are not part of, it means the sender (assuming using the latest version and not malicious) has not received our "leave" message.

In this case we need to display the option to retry leaving the group again and when leaving, send the "leave" message again to everyone in the current member list.

This is a known problem listed here:
https://github.com/chatmail/models/tree/main/group-membership#retry-messages
However, the proposed solution there is to collect the list of senders that keep sending us messages. Instead of collecting the list of senders who keep sending us the messages, it should be fine to send the message back to the whole memberlist to avoid maintaining another list.

On the library side we only need an API to tell whether this "retry leaving" option should be displayed somewhere. We should agree how to do this in the UI first so we don't implement unused APIs. Probably in the same place where we display the input and "accept"/"delete" buttons for contact requests.