Track views of the {profiles,groups}/billing page

- Add a shared track_experiment_events.js file
- Track 'view_billings_page' from either profiles or groups billing pg.
- Set the frontend_experimentation_tracking_data for our
  :contact_sales_btn_in_app experiment

ee/app/controllers/groups/billings_controller.rb

@@ -10,6 +10,7 @@ class Groups::BillingsController < Groups::ApplicationController
     @top_most_group = @group.root_ancestor if @group.has_parent?
     current_plan = (@top_most_group || @group).plan_name_for_upgrading
     @plans_data = FetchSubscriptionPlansService.new(plan: current_plan).execute
+    track_experiment_event(:contact_sales_btn_in_app, 'page_view:billing_plans:group')
     record_experiment_user(:contact_sales_btn_in_app)
   end
 end

ee/app/controllers/profiles/billings_controller.rb

@@ -7,6 +7,7 @@ class Profiles::BillingsController < Profiles::ApplicationController
     @plans_data = FetchSubscriptionPlansService
       .new(plan: current_user.namespace.plan_name_for_upgrading)
       .execute
+    track_experiment_event(:contact_sales_btn_in_app, 'page_view:billing_plans:profile')
     record_experiment_user(:contact_sales_btn_in_app)
   end
 end

ee/spec/controllers/groups/billings_controller_spec.rb

@@ -29,6 +29,7 @@ RSpec.describe Groups::BillingsController do
         allow_next_instance_of(FetchSubscriptionPlansService) do |instance|
           allow(instance).to receive(:execute)
         end
+        allow(controller).to receive(:track_experiment_event)
       end
 
       it 'renders index with 200 status code' do
@@ -49,6 +50,12 @@ RSpec.describe Groups::BillingsController do
         expect(assigns(:plans_data)).to eq(data)
       end
 
+      it 'tracks the page view for the contact_sales_btn_in_app experiment' do
+        expect(controller).to receive(:track_experiment_event).with(:contact_sales_btn_in_app, 'page_view:billing_plans:group')
+
+        get_index
+      end
+
       it 'records user for the contact_sales_btn_in_app experiment' do
         expect(controller).to receive(:record_experiment_user).with(:contact_sales_btn_in_app)
 

ee/spec/controllers/profiles/billings_controller_spec.rb

@@ -13,6 +13,7 @@ RSpec.describe Profiles::BillingsController do
       allow_next_instance_of(FetchSubscriptionPlansService) do |instance|
         allow(instance).to receive(:execute)
       end
+      allow(controller).to receive(:track_experiment_event)
     end
 
     def get_index
@@ -39,6 +40,12 @@ RSpec.describe Profiles::BillingsController do
       expect(assigns(:plans_data)).to eq(data)
     end
 
+    it 'tracks the page view for the contact_sales_btn_in_app experiment' do
+      expect(controller).to receive(:track_experiment_event).with(:contact_sales_btn_in_app, 'page_view:billing_plans:profile')
+
+      get_index
+    end
+
     it 'records user for the contact_sales_btn_in_app experiment' do
       expect(controller).to receive(:record_experiment_user).with(:contact_sales_btn_in_app)