Update coding style to include debug prefix for query configs

CODING_STYLE.md

@@ -62,7 +62,11 @@ line width, indentation and ordering (for includes, using directives and etc). 
   their public APIs. Only use test methods in rare edge cases where this is not
   possible. For example, MemoryAllocator::testingSetFailureInjection() is used
   to to inject various memory allocation failures to test error handling paths.
-
+* Use the **debug** prefix for query configs that are intended for debugging
+  purposes only. These configs may enable expensive checks or disable selective
+  code paths, and are not recommended for use in production environments. For
+  example, `debug_disable_expression_with_peeling` is used to disable peeling
+  optimization employed in expression evaluation.
 ## Comments
 
 Some good practices about code comments: