fix missing var

Author: deeikele

samples/microsoft/infrastructure-setup-terraform/00-basic/code/providers.tf

@@ -1,3 +1,4 @@
 # Setup providers
 provider "azapi" {
+  subscription_id = var.subscription_id
 }

samples/microsoft/infrastructure-setup-terraform/00-basic/code/variables.tf

@@ -2,3 +2,7 @@ variable "location" {
   description = "The name of the location to provision the resources to"
   type        = string
 }
+
+variable "subscription_id" {
+  type = string
+}