fix(terraform): Add missing VM configurations to tfvars example

Added VM configuration objects for all three nodes:
- k3s_server_1_config: 6 cores, 12GB RAM, 100G disk
- k3s_server_2_config: 6 cores, 12GB RAM, 100G disk
- etcd_witness_config: 2 cores, 2GB RAM, 20G disk

Removed undeclared 'management_bridge' variable that was causing
warnings in terraform plan.

This allows terraform plan to execute successfully in CI with
the example configuration file.

terraform/terraform.tfvars.example

@@ -23,6 +23,27 @@ snippets_storage    = "local"
 
 # Network
 k3s_network_bridge = "k3s"
-management_bridge  = "vmbr0"
 k3s_gateway        = "10.100.20.1"
 k3s_dns            = ["10.100.20.1", "1.1.1.1"]
+
+# VM Configurations
+k3s_server_1_config = {
+  ip        = "10.100.20.10/24"
+  cores     = 6
+  memory    = 12288
+  disk_size = "100G"
+}
+
+k3s_server_2_config = {
+  ip        = "10.100.20.20/24"
+  cores     = 6
+  memory    = 12288
+  disk_size = "100G"
+}
+
+etcd_witness_config = {
+  ip        = "10.100.20.30/24"
+  cores     = 2
+  memory    = 2048
+  disk_size = "20G"
+}