Expose ActiveStorage::Analyzer#logger in API docs [ci skip]

Clarify that it's public API and may be used in third-party analyzers.

activestorage/lib/active_storage/analyzer.rb

@@ -26,7 +26,7 @@ def metadata
     end
 
     private
-      def logger
+      def logger #:doc:
         ActiveStorage.logger
       end
   end