container: add skip_node_pool_refresh to google_container_cluster data source

[ralbertazzi]

Fixes hashicorp/terraform-provider-google#29171

Description

The skip_node_pool_refresh performance flag added to the google_container_cluster resource in #17968 is not usable from the corresponding data source: DatasourceSchemaFromResourceSchema copies every resource field as computed-only, so the flag exists on the data source but cannot be set.

The data source read path already honors the flag — datasourceContainerClusterRead delegates to resourceContainerClusterRead, which skips the node pool flattening in flattenClusterNodePools when the flag is set. This PR makes the field settable via AddOptionalFieldsToSchema, so users with clusters that have a high node pool count can opt out of the node pool read:

data "google_container_cluster" "my_cluster" {
  name     = "my-cluster"
  location = "us-east1-a"

  skip_node_pool_refresh = true
}

When enabled, the data source's node_pool attribute remains empty ([]), matching the resource-side behavior.

Testing

• Generated the google provider locally and confirmed the diff is scoped to the data source, its test, and the data source docs
• Provider builds and go vet/go test ./google/services/container/ pass (including TestUnitFlattenClusterNodePools)
• A local check confirmed the generated data source schema marks skip_node_pool_refresh as Optional while node_pool stays computed-only
• Added TestAccContainerClusterDatasource_skipNodePoolRefresh, mirroring the existing data source tests, which asserts node_pool.# = 0 when the flag is set (requires a real GCP project / VCR cassette to run)

Release Note Template for Downstream PRs (will be copied)

See Write release notes for guidance.

container: added `skip_node_pool_refresh` field to `google_container_cluster` data source. When set to true, the data source skips reading node pools from the API, resolving long read times on clusters with a large number of node pools. Note that this results in `node_pool` being set to an empty list

🤖 Generated with OpenCode (GPT-5.6 Terra)

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