Update DQN Colab example to support export for Barracuda inference (#5643)

* Update DQN GridWorld colab example to be capable of outputting an ONNX model that works for inference.
-Allow GridWorld to work without a GoalSensor.  Defaults to the GreenPlus target in that case.
-Add GridWorldColab.onnx file, trained and generated with the colab.

* Upgrade DQN GridWorld Colab to produce model that can work with (modified) GridWorld Scene.
-permute observation images from NHWC to NCHW right after env_step.  Everything following is NCHW.
-update input_shape indexes and remove equivalent permute from the VisualQNetwork
-fix reference to global qnet inside generate_trajectories (use the passed in version)
-create wrapper network to add required constants and dummy input masks required by the
 runtime inference (Barracuda)
-export the wrapped network to ONNX format compatible with Barracuda

* Add additional GridWorld scene called GridWorldColab that has the goal sensors removed (target is always green plus) and masks disabled.  The purpose of this is to have a scene compatible with the DQN GridWorld Colab example.

* Minor edit in Colab docs.

* Delete unnecessary .lighting file.

* Update changelog.

* Update colab/Colab_UnityEnvironment_2_Train.ipynb

Co-authored-by: Maryam Honari <[email protected]>

* Fix error in colab metadata name.

* Add suggested comments and fix incorrect parameter ordering.

* Update docs for Elo curriculum completion measure.

Co-authored-by: Maryam Honari <[email protected]>

Author: jrupert-unity