refactor: Replace HubsConstants.googlePlacesApiKey with AppConfig.googlePlacesApiKey for better configuration management

apps/mobile/packages/core/lib/src/config/app_config.dart

@@ -1,5 +1,9 @@
+/// AppConfig class that holds configuration constants for the application.
+/// This class is used to access various API keys and other configuration values
+/// throughout the app.
 class AppConfig {
   AppConfig._();
 
+  /// The Google Places API key used for address autocomplete functionality.
   static const String googlePlacesApiKey = String.fromEnvironment('GOOGLE_PLACES_API_KEY');
 }