[NEP-18090]: Adding en endpoint for warming up the dataset cache

Spec failure fixes

Author: soundarya-mv

lib/superset/dataset/warm_up_cache.rb

@@ -10,6 +10,10 @@ def initialize(dashboard_id:)
 
       def perform
         validate_dashboard_id
+        response
+      end
+
+      def response
         dataset_details = fetch_dataset_details(dashboard_id)
         dataset_details.each do |dataset|
           begin
@@ -18,7 +22,6 @@ def perform
             Rollbar.error(e.message)
           end 
         end
-        return "Dashboard warmed up" 
       end
 
       def validate_dashboard_id