Set timestamp for every DataMessage (#290)

This imitates the behaviour of Signal-Desktop and is required to pass envelope content validation. Previous reactions would emit this field.

Co-authored-by: Gabriel Féron <[email protected]>

presage/src/manager/registered.rs

@@ -869,6 +869,7 @@ impl<S: Store> Manager<S, Registered> {
                 .profile_key
                 .get_or_insert(self.state.data.profile_key().get_bytes().to_vec());
             message.required_protocol_version = Some(0);
+            message.timestamp = Some(timestamp);
         }
 
         sender