Update metrics_handler requirements file to include kubernetes
Update metrics_handler requirements file to include kubernetes

Change-Id: I8d5a53ff59cc06fa49c4700197881e1190c7a21d
Reviewed-on: https://team-review.git.corp.google.com/c/cloud-accelerators-ml/xl-ml-test/+/654785
Reviewed-by: Zachary Cain <f7db6f5f18ec3d1176d7b7f440bd23720036cea8@google.com>

GoogleCloudPlatform/ml-testing-accelerators,GoogleCloudPlatform/ml-testing-accelerators