Fix diff suppress function ignoring additive_vpc_scope_dns_domain in Autopilot clusters

[modular-magician]

self-appointed successor to #11744

GKE Autopilot allows setting additive VPC scope domain on creation only. However, current implementation of the diff suppress function for Autopilot clusters removes any values in dns_config of Autopilot clusters, all the time.

This change permits setting additive VPC scope domain.

Remaining action items:

• validate that allowing dns_config.# doesn't cause issues (it seems necessary for dns_config.0.additive_vpc_scope_dns_domain to exist
• revise test coverage to look for other gaps
• verify that the change in google_storage_transfer_job shows permanently diff when transfer_options set all false explicitly. #11744 to ForceNew when domain changes is exactly the behavior we want and copy it over
• write the release note below

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container: fixed `additive_vpc_scope_dns_domain` being ignored in Autopilot cluster definition

Derived from GoogleCloudPlatform/magic-modules#12567