fgt_asg: some deployments fail with VPC connector error

[bartekmo]

In some cases deployment fails with error
"A Connector must specify either max_throughput or max_instances" in
function.tf 153: resource "google_vpc_access_connector" "vpc_connector"

Plan does not have any value for max_throughput or max_instances.

Although not defined in the function.tf code, deploying example code does add values for max_throughput and max_instances into terraform plan