Add differentiation for tracking purchases

- The SubscriptionsController is used for SaaS subscriptions and add-ons
  as well. In order to be able to differentiate these in data analytics
  down the line we need to mark when an add-on was purchased and when it
  was a subscription.

- refs:
  https://gitlab.com/gitlab-data/product-analytics/-/issues/158
  https://gitlab.com/gitlab-data/product-analytics/-/issues/158#note_842168023
  https://gitlab.com/gitlab-org/gitlab/-/issues/342853

ee/app/controllers/subscriptions_controller.rb

 # frozen_string_literal: true
 
 class SubscriptionsController < ApplicationController
+  SUCCESS_SUBSCRIPTION = 'Success: subscription'
+  SUCCESS_ADDON = 'Success: add-on'
   include InternalRedirect
   include OneTrustCSP
 
@@ -103,7 +105,7 @@ class SubscriptionsController < ApplicationController
     ).execute
 
     if response[:success]
-      track_purchase message: 'Success', namespace: group
+      track_purchase message: track_success_message, namespace: group
       response[:data] = { location: redirect_location(group) }
     else
       track_purchase message: response.dig(:data, :errors), namespace: group
@@ -123,6 +125,14 @@ class SubscriptionsController < ApplicationController
     )
   end
 
+  def track_success_message
+    addon? ? SUCCESS_ADDON : SUCCESS_SUBSCRIPTION
+  end
+
+  def addon?
+    Gitlab::Utils.to_boolean(subscription_params[:is_addon], default: false)
+  end
+
   def redirect_location(group)
     return safe_redirect_path(params[:redirect_after_success]) if params[:redirect_after_success]
 

ee/spec/controllers/subscriptions_controller_spec.rb

@@ -451,7 +451,26 @@ RSpec.describe SubscriptionsController do
                 category: 'SubscriptionsController',
                 label: 'confirm_purchase',
                 action: 'click_button',
-                property: 'Success',
+                property: 'Success: subscription',
+                namespace: selected_group,
+                user: user
+              )
+            end
+          end
+
+          context 'purchasing an addon' do
+            before do
+              params[:subscription][:is_addon] = true
+            end
+
+            it 'tracks creation with add-on success message' do
+              subject
+
+              expect_snowplow_event(
+                category: 'SubscriptionsController',
+                label: 'confirm_purchase',
+                action: 'click_button',
+                property: 'Success: add-on',
                 namespace: selected_group,
                 user: user
               )