FIX: Trigger user_logged_out event when the user logs out (#28482)

What did this fix?
===============

Previously, we only triggered this event in the `user.logged_out` method.
This resulted in the event being triggered only when the user was logged
out by the administrator or the site had strict logout mode enabled.
This bug affected customers who managed user status via webhooks.

meta topic: https://meta.discourse.org/t/user-log-out-event-not-triggered-in-webhooks/249464

lib/auth/default_current_user_provider.rb

@@ -338,6 +338,7 @@ class Auth::DefaultCurrentUserProvider
       user.logged_out
     elsif user && @user_token
       @user_token.destroy
+      DiscourseEvent.trigger(:user_logged_out, user)
     end
 
     cookie_jar.delete("authentication_data")

spec/lib/auth/default_current_user_provider_spec.rb

@@ -736,13 +736,14 @@ RSpec.describe Auth::DefaultCurrentUserProvider do
   end
 
   describe "#log_off_user" do
-    it "should work when the current user was cached by a different provider instance" do
+    let(:env) do
       user_provider = provider("/")
       user_provider.log_on_user(user, {}, user_provider.cookie_jar)
       cookie = CGI.escape(user_provider.cookie_jar["_t"])
-      env =
-        create_request_env(path: "/").merge({ :method => "GET", "HTTP_COOKIE" => "_t=#{cookie}" })
+      create_request_env(path: "/").merge({ :method => "GET", "HTTP_COOKIE" => "_t=#{cookie}" })
+    end
 
+    it "should work when the current user was cached by a different provider instance" do
       user_provider = TestProvider.new(env)
       expect(user_provider.current_user).to eq(user)
       expect(UserAuthToken.find_by(user_id: user.id)).to be_present
@@ -751,6 +752,18 @@ RSpec.describe Auth::DefaultCurrentUserProvider do
       user_provider.log_off_user({}, user_provider.cookie_jar)
       expect(UserAuthToken.find_by(user_id: user.id)).to be_nil
     end
+
+    it "should trigger user_logged_out event" do
+      event_triggered_user = nil
+      event_handler = Proc.new { |user| event_triggered_user = user.id }
+      DiscourseEvent.on(:user_logged_out, &event_handler)
+
+      user_provider = TestProvider.new(env)
+      user_provider.log_off_user({}, user_provider.cookie_jar)
+      expect(event_triggered_user).to eq(user.id)
+
+      DiscourseEvent.off(:user_logged_out, &event_handler)
+    end
   end
 
   describe "first admin user" do