Add feature flags on budget controllers

Although we had this feature flag in most places, we forgot to add it in
some of the controllers.

app/controllers/management/budgets/investments_controller.rb

@@ -1,5 +1,8 @@
 class Management::Budgets::InvestmentsController < Management::BaseController
   include Translatable
+  include FeatureFlags
+  feature_flag :budgets
+
   before_action :load_budget
 
   load_resource :budget