FIX: Prevent infinite loop of automations triggering each other (#26814)

It's currently possible to setup multiple automation rules that trigger each other resulting in an infinite loop. To prevent that, this commit adds a global "circuit breaker" that prevents all automations from triggering while an automation rule is executing.

Internal topic: t/124365.

plugins/automation/spec/integration/infinite_loop_protection_spec.rb

@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+require_relative "../discourse_automation_helper"
+
+describe "Infinite loop protection" do
+  fab!(:automation_1) do
+    Fabricate(:automation, script: "auto_responder", trigger: "post_created_edited", enabled: true)
+  end
+
+  fab!(:automation_2) do
+    Fabricate(:automation, script: "auto_responder", trigger: "post_created_edited", enabled: true)
+  end
+
+  before do
+    SiteSetting.discourse_automation_enabled = true
+
+    automation_1.upsert_field!(
+      "word_answer_list",
+      "key-value",
+      { value: [{ key: "", value: "this is the reply" }].to_json },
+    )
+    automation_2.upsert_field!(
+      "word_answer_list",
+      "key-value",
+      { value: [{ key: "", value: "this is the reply" }].to_json },
+    )
+
+    automation_1.upsert_field!(
+      "answering_user",
+      "user",
+      { value: Fabricate(:user).username },
+      target: "script",
+    )
+    automation_2.upsert_field!(
+      "answering_user",
+      "user",
+      { value: Fabricate(:user).username },
+      target: "script",
+    )
+  end
+
+  it "prevents infinite loop of 2 auto_responder automations triggering each other" do
+    expect do
+      PostCreator.create!(Fabricate(:user), raw: "post", title: "topic", skip_validations: true)
+    end.to change { Post.count }.by(3)
+  end
+end