chore: improve plan-based feature handling with plan hierarchy (#11335)

- Refactor HandleStripeEventService to better manage features by plan
- Add constants for features available in each plan tier (Startup,
Business, Enterprise)
- Add channel_instagram to Startup plan features
- Improve downgrade handling to properly disable higher-tier features
- Clean up and optimize tests for maintainability
- Add comprehensive test coverage for plan upgrades and downgrades

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Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

enterprise/app/controllers/super_admin/enterprise_base_controller.rb

@@ -1,8 +1,2 @@
 class SuperAdmin::EnterpriseBaseController < SuperAdmin::ApplicationController
-  before_action :prepend_view_paths
-
-  # Prepend the view path to the enterprise/app/views won't be available by default
-  def prepend_view_paths
-    prepend_view_path 'enterprise/app/views/'
-  end
 end