[FSSDK-9509] Update http_project_config_manager.rb with soft log warning about polling interval < 30s (#338)

* Update http_project_config_manager.rb

Add soft warning that polling interval under 30 s is not recommended.

* Update w single quotes

* Update http_project_config_manager.rb

* Update WARNING to WARN

* Update lib/optimizely/config_manager/http_project_config_manager.rb

Co-authored-by: Andy Leap <104936100+andrewleap-optimizely@users.noreply.github.com>

---------

Co-authored-by: Andy Leap <104936100+andrewleap-optimizely@users.noreply.github.com>

Author: Mat001

lib/optimizely/config_manager/http_project_config_manager.rb

@@ -268,6 +268,13 @@ def polling_interval(polling_interval)
         return
       end
 
+      if polling_interval < 30
+        @logger.log(
+          Logger::WARN,
+          'Polling intervals below 30 seconds are not recommended.'
+        )
+      end
+
       @polling_interval = polling_interval
     end