fix volume metadata syntax

main.tf

@@ -57,7 +57,7 @@ output "keypair_name" {
 data "openstack_networking_network_v2" "external_net" {name = var.external_network}
 data "openstack_blockstorage_volume_v2" "disk" {
   name = "var.data_volume"
-  metadata =  "id:volume_id"
+  metadata = { id = "volume_id" }
 }
 
 # runs the ohpc-instance module - creates ohpc instance using variables defined above