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>

app/controllers/super_admin/accounts_controller.rb

@@ -66,3 +66,5 @@ class SuperAdmin::AccountsController < SuperAdmin::ApplicationController
     # rubocop:enable Rails/I18nLocaleTexts
   end
 end
+
+SuperAdmin::AccountsController.prepend_mod_with('SuperAdmin::AccountsController')