Per the [RFC](https://github.com/tensorflow/community/blob/393dfc9e03dd4150a839de6357a26e0259aa97d6/rfcs/20181214-move-to-addons.md), we need to move [MovingAverageOptimizer](https://github.com/tensorflow/tensorflow/blob/v1.12.0/tensorflow/contrib/opt/python/training/moving_average_optimizer.py) from contrib to addons: This will involve inheriting from base Keras optimizer, modifying the code to match those APIs, and modifying test cases to run in TF2.