UX: logs when an automation is destroyed (#29565)

A `UserHistory` entry will now be created when an automation is destroyed. This is visible in `/admin/logs/staff_action_logs`. id, name, trigger and script will be logged.

This commit also creates a service `DestroyAutomation` to hold all the destroy automation logic.

---------
Co-authored-by: Martin Brennan <mjrbrennan@gmail.com>

plugins/automation/app/services/discourse_automation/destroy_automation.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+module DiscourseAutomation
+  class DestroyAutomation
+    include ::Service::Base
+
+    # @!method self.call(guardian:, params:)
+    #   @param [Guardian] guardian
+    #   @param [Hash] params
+    #   @option params [Integer] :automation_id
+    #   @return [Service::Base::Context]
+    params do
+      attribute :automation_id, :integer
+      validates :automation_id, presence: true
+    end
+
+    model :automation
+    policy :can_destroy_automation
+    transaction do
+      step :log_action
+      step :destroy_automation
+    end
+
+    private
+
+    def fetch_automation(params:)
+      DiscourseAutomation::Automation.find_by(id: params.automation_id)
+    end
+
+    def can_destroy_automation(guardian:)
+      guardian.is_admin?
+    end
+
+    def log_action(automation:, guardian:)
+      StaffActionLogger.new(guardian.user).log_custom(
+        "delete_automation",
+        id: automation.id,
+        name: automation.name,
+        script: automation.script,
+        trigger: automation.trigger,
+      )
+    end
+
+    def destroy_automation(automation:)
+      automation.destroy!
+    end
+  end
+end