Compute VM module refactor (#3805)

* add ad for compute-vm refactor

* Exclue nic_type from validated fields, add split of main.tf and template.tf

* boot disk

* fix examples and fixtures

* attached disks

* fix further examples and module-level tests

* remove extra file

* fix mig examples

* finish refactoring variables

* align fast and other modules

* refactor(compute-vm): align examples and ADR with the newly implemented interface

This commit addresses the remaining references of the `instance_type` and `confidential_compute` parameters in the testing environment and updates the ADR.

* feat(compute-vm): add network_performance_config to instance and templates

This change implements the usage of the `network_performance_tier` variable we added earlier into the actual Terraform resources.

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Co-authored-by: Wiktor Niesiobędzki <wiktorn@google.com>

modules/vpc-sc/README.md

@@ -210,7 +210,7 @@ The caller must have `cloudasset.assets.searchAllResources` permission to perfor
 module "vpc-sc" {
   source                  = "./fabric/modules/vpc-sc"
   project_id_search_scope = var.org_id
-  access_policy = "12345678"
+  access_policy           = "12345678"
   ingress_policies = {
     i1 = {
       from = {