move multi-network to GA

[modular-magician]

This PR is to add terraform support for Multi-network GA on GKE cluster.

The Multi-network in Terraform beta was added to the magic module in the PR #8385.
This PR basically moves the enable_multi_networking field in google_container_cluster and additional_node_network_configs additional_pod_network_configs fields in google_container_node_pool to GA.

Release Note Template for Downstream PRs (will be copied)

container: promoted `enable_multi_networking` to GA in the `google_container_cluster` resource

container: promoted `additional_node_network_configs` and `additional_pod_network_configs` fields to GA in the `google_container_node_pool` resource

Derived from GoogleCloudPlatform/magic-modules#11062

[github-actions]

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