Prevent unnecessary "bastion_vm" replacement when upgrading to 9.x version

[FabrizioCafolla]

Description

This PR fixes an issue in version 9.0.0 where adding params block to an existing bastion host instance would force unnecessary VM replacement.

Problem

In the current implementation, the params block is always present in the google_compute_instance_from_template.bastion_vm resource, which causes Terraform to force replacement of the VM when resource_manager_tags are added to an existing instance:

# module.iap_bastion_host.google_compute_instance_from_template.bastion_vm[0] must be replaced
-/+ resource "google_compute_instance_from_template" "bastion_vm" {
  ...
+ params { # forces replacement
    + resource_manager_tags = (known after apply)
  }
  ...
}

Solution

The fix implements a dynamic "params" block that only creates the params configuration when var.resource_manager_tags is not null. This prevents unnecessary VM destruction and recreation when resource manager tags are added or modified.