feat(azure): add optional timer schedule for container build

Author: matt-FFFFFF

modules/azure/container_registry.tf

@@ -36,6 +36,11 @@ resource "azurerm_container_registry_task" "alz" {
   identity {
     type = "SystemAssigned" # Note this has to be a System Assigned Identity to work with private networking and `network_rule_bypass_option` set to `AzureServices`
   }
+  timer_trigger {
+    name     = "scheduled-build"
+    schedule = var.container_registry_task_timer_trigger_schedule
+    enabled  = var.container_registry_task_timer_trigger_enabled
+  }
   registry_credential {
     custom {
       login_server = azurerm_container_registry.alz[0].login_server

modules/azure/variables.tf

@@ -498,6 +498,30 @@ variable "container_registry_image_tag" {
   default     = "{{.Run.ID}}"
 }
 
+variable "container_registry_task_timer_trigger_enabled" {
+  description = <<-EOT
+    **(Optional, default: `true`)** Enable daily timer trigger for container registry image builds.
+
+    When enabled, the ACR task runs daily to rebuild the agent image,
+    ensuring it stays up-to-date with latest patches and dependencies.
+    
+    See container_registry_task_timer_trigger_schedule for customizing the schedule.
+  EOT
+  type        = bool
+  default     = true
+}
+
+variable "container_registry_task_timer_trigger_schedule" {
+  description = <<-EOT
+    **(Optional, default: `"0 0 * * 0"`)** CRON schedule for the container registry task timer trigger.
+
+    Default schedule runs at midnight on Sundays.
+    Modify as needed to fit maintenance windows or update frequency.
+  EOT
+  type        = string
+  default     = "0 0 * * 0"
+}
+
 variable "use_self_hosted_agents" {
   description = <<-EOT
     **(Optional, default: `true`)** Controls whether to deploy self-hosted CI/CD agents in Azure Container Instances.