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>

config/application.rb

@@ -44,6 +44,8 @@ module Chatwoot
     # rubocop:disable Rails/FilePath
     config.eager_load_paths += Dir["#{Rails.root}/enterprise/app/**"]
     # rubocop:enable Rails/FilePath
+    # Add enterprise views to the view paths
+    config.paths['app/views'].unshift('enterprise/app/views')
 
     # Settings in config/environments/* take precedence over those specified here.
     # Application configuration can go into files in config/initializers