Add cpu_utilization and concurrency_utilization to Cloud Run v2 service revision scaling (beta)

[yotamobol]

Fixes hashicorp/terraform-provider-google#28324

Cloud Run added custom scaling controls in Preview on April 16, 2026 (release note). The Cloud Run Admin API v2 exposes them as template.scaling.cpuUtilization and template.scaling.concurrencyUtilization (GoogleCloudRunV2RevisionScaling, per the v2 discovery document), but the provider's revision scaling block only supports min_instance_count/max_instance_count, and the v2 API rejects the v1-style run.googleapis.com/scaling-* annotations — so these targets currently cannot be managed with Terraform at all.

This PR adds both fields to google_cloud_run_v2_service:

• template.scaling.cpu_utilization (Double, beta-only)
• template.scaling.concurrency_utilization (Double, beta-only)

Design notes for review:

• min_version: 'beta' — the underlying feature is in Preview (configured via gcloud beta run services update --scaling-cpu-target/--scaling-concurrency-target).
• No send_empty_value — the API uses 0.0 to disable a scaling driver and rejects requests where both drivers are disabled. Sending zero values for unset fields would therefore break every existing configuration that omits them. Consequence: explicitly setting 0.0 in config to disable a driver is not expressible with this change; happy to add custom expand logic if maintainers prefer supporting that case.
• default_from_api: true — the server controls the effective default (0.6) and the fields are part of an opt-in surface; this avoids permadiffs when unset.
• Fields are scoped to google_cloud_run_v2_service only; the gcloud/docs surface for this Preview is services-only (worker pools are not mentioned).
• Added a beta acceptance test (TestAccCloudRunV2Service_cloudrunv2ServiceWithScalingUtilizationTargets) covering create (0.5/0.5), update (0.8/0.7), and import, modeled on the existing manual-scaling test in the same file.

Release Note Template for Downstream PRs (will be copied)

cloudrunv2: added `template.scaling.cpu_utilization` and `template.scaling.concurrency_utilization` fields to `google_cloud_run_v2_service` resource (beta)

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[github-actions]

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