fix(container): fix a bug in GKE blue green upgrade policy

[modular-magician]

This is fixing the issue reported in hashicorp/terraform-provider-google#25757.
Fixes hashicorp/terraform-provider-google#25757

The validation code previously take an empty list as a configured value. And therefore incorrectly think the standard_rollout_policy and autoscaled_rollout_policy.

Verification:

1. Created a tf file to reproduce the problem.
2. Change the code and built a provider locally.
3. Verify the new provider doesn't have this bug anymore.

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container: fixed a bug in `google_container_node_pool` that prevented creation when `blue_green_settings` was specified

Derived from GoogleCloudPlatform/magic-modules#16239