code: public void addParticipants(@NonNull final String conversationId, @NonNull final List<Participant> participants, @Nullable Callback<ComapiResult<Void>> callback) {
          adapter.adapt(addParticipants(conversationId, participants), callback);
      }
docs: Returns observable to add a list of participants to a conversation.
  
  @param conversationId ID of a conversation to update.
  @param participants   New conversation participants details.
  @param callback       Callback to deliver new session instance.