Add correction message to inform slave about QoS Controller actions

message QoSCorrection {
  // NOTE: In future we can define more actions like
  // resize or freeze, but for now we have:
  // 1) kill - terminate the executor or task
  enum Type {
    KILL = 1;
  }
  //Kill action which will be performed on an executor
  message Kill {
    optional ExecutorID executor_id = 1;
  }

  required Type action = 1;
  optional string reason = 2;
  optional double timestamp = 3;
  optional Kill kill = 4;
}