class_docstr: Observe the number of elapsed steps in an episode.
  
  A new observation will be a tuple of an original observation and an integer
  that is equal to the elapsed steps in an episode.
code: def step(self, action):
      observation, reward, done, info = self.env.step(action)
      self._elapsed_steps += 1
      assert self._elapsed_steps <= self._max_steps
      return (observation, self._elapsed_steps), reward, done, info
  
imports: import argparse
  import functools
  import os
  import chainer
  from chainer import functions
  from chainer import links
  from chainer import optimizers
  import gym
  import gym.spaces
  import numpy
  import chainerrl
  from chainerrl.action_value import DiscreteActionValue
  from chainerrl import experiments
  from chainerrl import explorers
  from chainerrl import misc
  from chainerrl import replay_buffer
label_desc: Use image node_id 3 for calling the ObserveElapsedSteps obj's underlying member method code with example usage: obj.step(action) and returns: observation,  self,  reward,  done,  info