Standardize all optimizer serialization checks

[seanpmorgan]

Part of #992. We need to crate a common serialization check for optimizers similar to check_metrics_serialization:
https://github.com/tensorflow/addons/blob/master/tensorflow_addons/testing/serialization.py#L10

Ideally this will extend the base check_config method, but we noticed in #1728 that there are some issues that need to be adressed.

After this is complete we can move on to serialization checks for all submodules.

[tacho090]

I'm interested in helping. Could you assign this to me please?

[seanpmorgan]

TensorFlow Addons is transitioning to a minimal maintenance and release mode. New features will not be added to this repository. For more information, please see our public messaging on this decision:
TensorFlow Addons Wind Down

Please consider sending feature requests / contributions to other repositories in the TF community with a similar charters to TFA:
Keras
Keras-CV
Keras-NLP