code: public void updateConversation(@NonNull final String conversationId, @NonNull final ConversationUpdate request, @NonNull final String eTag, @Nullable Callback<ComapiResult<ConversationDetails>> callback) {
          adapter.adapt(updateConversation(conversationId, request, eTag), callback);
      }
docs: Returns observable to update a conversation.
  
  @param conversationId ID of a conversation to update.
  @param request        Request with conversation details to update.
  @param eTag           ETag for server to check if local version of the data is the same as the one the server side.
  @param callback       Callback to deliver new session instance.