code: public void register(final long masterId, final List<ConfigProperty> configList)
        throws IOException {
      retryRPC(() -> {
        mClient.registerMaster(RegisterMasterPRequest.newBuilder().setMasterId(masterId)
            .setOptions(RegisterMasterPOptions.newBuilder().addAllConfigs(configList).build())
            .build());
        return null;
      });
    }
docs: Registers with the leader master.
  
  @param masterId the master id of the standby master registering
  @param configList the configuration of this master