gcp: support projects with no default permissions (#3656)

* helm/gcp: use service account in operator and joinservice

* helm: format operator testdata

* terraform/iam: create additional service account for VMs

This service account is used in the following commits and is attached to the VMs

* config: pass VM service account from iam create to cluster create via config

* cli/iamcreate: limit name prefix length

* docs: add minimal gcp IAM permissions

terraform/infrastructure/gcp/modules/instance_group/variables.tf

@@ -108,3 +108,9 @@ variable "cc_technology" {
     error_message = "The confidential computing technology has to be 'SEV' or 'SEV_SNP'."
   }
 }
+
+variable "iam_service_account_vm" {
+  type        = string
+  default     = ""
+  description = "IAM service account used for the VMs"
+}