Override `get_config` in custom Keras metrics to include all args in `__init__`.
Override `get_config` in custom Keras metrics to include all args in `__init__`.

So the metrics can be constructable when building a `tff.learning.Model` from a Keras model using `from_keras_model`.

PiperOrigin-RevId: 410362543
Change-Id: Ie3337f884a8e038ec5311c45900d1433e1f1e7bc

google-research/federated,google-research/federated