Enhance Azure example configurations: add subscription_id and tenant_id variables, update terraform.tfvars.example, and refine .gitignore for tfplan files

.gitignore

@@ -8,6 +8,7 @@ __pycache__
 .vscode
 tmp
 .terraform*
+*tfplan*
 *.tfstate
 *.tfstate.*
 *.auto.tfvars

examples/azure/providers.tf

@@ -1,3 +1,6 @@
 provider "azurerm" {
   features {}
+
+  subscription_id = var.subscription_id
+  tenant_id       = var.tenant_id != "" ? var.tenant_id : null
 }

examples/azure/terraform.tfvars.example

@@ -2,6 +2,7 @@
 # Keep secrets - psk here - out of any tracked file: set them with
 # TF_VAR_psk or in a git-ignored *.auto.tfvars instead.
 
+subscription_id       = "00000000-0000-0000-0000-000000000000"
 location              = "westeurope"
 name                  = "vpn-router-example"
 admin_ssh_public_key  = "ssh-ed25519 AAAA... you@example.com"

examples/azure/variables.tf

@@ -1,3 +1,14 @@
+variable "subscription_id" {
+  description = "Azure subscription ID to deploy into."
+  type        = string
+}
+
+variable "tenant_id" {
+  description = "Azure AD tenant ID. Leave empty to use the tenant of the credentials Terraform is running with."
+  type        = string
+  default     = ""
+}
+
 variable "location" {
   description = "Azure region to deploy into."
   type        = string