Autoscaler maxreplicas fix

[modular-magician]

This PR removes unnecessary requirements reported in hashicorp/terraform-provider-google#18332.

This was an inconsistency, since in both terraform registry and Google Cloud documentation it's not specified that the value cannot be 0.

Google Cloud API gives you ability to create Autoscaler or Regional Autoscaler which have both minReplicas and maxReplicas set to 0. I've created one in Google Cloud Console and it worked just fine.

For the reported issue , I checked and request was missing max_num_replica field. For both zonal and regional autoscaler resources, I checked and min_num_replica field has send_empty_value set, while max_num_replica field doesn't. If we read the documentation of send_empty_value, this is the reason why max_num_replica was omitted entirely from the API request, when it was set to 0.

Fixes hashicorp/terraform-provider-google#18332

compute: fixed a bug preventing the creation of `google_compute_autoscaler` and `google_compute_region_autoscaler` resources if both `maxReplicas` and `minReplicas` were configured as zero.

Derived from GoogleCloudPlatform/magic-modules#11083