public static PipeDataNodePluginAgent plugin() {
    return PipeDataNodeAgentHolder.HANDLE.pipeDataNodePluginAgent;
  }
Get the singleton instance of {@link PipeDataNodePluginAgent}.

@return the singleton instance of {@link PipeDataNodePluginAgent}
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/pipe/agent/PipeDataNodeAgent.java