Changelog for goal conditioning (#5195)

* Changelog for goal conditioning

* adding a line about the changes to the gridworld example

* Addressing comments

* Change capitalization

com.unity.ml-agents/CHANGELOG.md

 - Make com.unity.modules.physics and com.unity.modules.physics2d optional dependencies. (#5112)
 - The default `InferenceDevice` is now `InferenceDevice.Default`, which is equivalent to `InferenceDevice.Burst`. If you
 depend on the previous behavior, you can explicitly set the Agent's `InferenceDevice` to `InferenceDevice.CPU`. (#5175)
+ - Added support for `Goal Signal` as a type of observation. Trainers can now use HyperNetworks to process `Goal Signal`. Trainers with HyperNetworks are more effective at solving multiple tasks. (#5142, #5159, #5149)
+ - Modified the [GridWorld environment](https://github.com/Unity-Technologies/ml-agents/blob/main/docs/Learning-Environment-Examples.md#gridworld) to use the new `Goal Signal` feature. (#5193)
 
 #### ml-agents / ml-agents-envs / gym-unity (Python)