Add a specific tile in the unencrypted room history

### Your use case

The Element-Web client displays a tile at the beginning of the unencrypted room in order to highlight the encryption is disabled

Element-Android displays currently this kind of tile only for the encrypted rooms:

This limitation on Element-Android may be due to the fact that the tile management is totally linked to the `m.room.encryption` state event. The unencrypted rooms don't have this kind of state event.
I suggest here displaying at the beginning of the unencrypted rooms the same tile as Element-Web. A new tile should be displayed in this room history when the room admin turns on the encryption.

Note: in Element-web the tile is not displayed in unencrypted room if the join_rule is public (the room is accessible by link)