add iam workload identity pool provider

[modular-magician]

Follow up to #4071 to also add google_iam_workload_identity_pool_provider resource to complete the two resourced needed for the new Google Cloud Workload Identity Federation feature.

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`google_iam_workload_identity_pool_provider`

Can this mark to fixes hashicorp/terraform-provider-google#7455 ??
Or should we hold on closing that issue until the two new data sources are created (or are these not needed?)

Derived from GoogleCloudPlatform/magic-modules#4129