Added private origin authentication for cloud cdn 'compute_backend_service'

[matheusaleixo-cit]

Adds support to 'aws_v4_authentication' and it's nested fields to 'compute_backend_service' resource.

Fixes: https://github.com/hashicorp/terraform-provider-google/issues/18551

Release Note Template for Downstream PRs (will be copied)

compute: added 'aws_v4_authentication' fields to 'google_compute_backend_service' resource;