cloudrunv2: Validate number of ports specified restricting to 1.

[modular-magician]

Accidentally specifying the containers.ports twice results in the following error:

Error: Error updating Service "projects/myproject/locations/us-central1/services/myservice": googleapi: Error 400: Violation in UpdateServiceRequest.service.template.containers[0].ports: ports should contain 0 or 1 port.
│ Details:
│ [
│   {
│     "@type": "type.googleapis.com/google.rpc.BadRequest",
│     "fieldViolations": [
│       {
│         "description": "ports should contain 0 or 1 port.",
│         "field": "Violation in UpdateServiceRequest.service.template.containers[0].ports"
│       }
│     ]
│   }
│ ]
│ 
│   with google_cloud_run_v2_service.myservice,
│   on myservice.tf line 1, in resource "google_cloud_run_v2_service" "myservice":
│    1: resource "google_cloud_run_v2_service" "myservice" {
│ 

It would be convenient if this issue could be caught at validation time.

cloudrunv2: added the validation to restrict number of ports to 1 to fail earlier than server-side validation

Derived from GoogleCloudPlatform/magic-modules#10173

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