rename sanitization instrumentation key

Author: gjtorikian

lib/html_pipeline.rb

@@ -187,7 +187,7 @@ def call(text, context: {}, result: {})
       end
     end
 
-    instrument("html_pipeline.sanitization", payload) do
+    instrument("sanitization.html_pipeline", payload) do
       result[:output] = Selma::Rewriter.new(sanitizer: @sanitization_config, handlers: @node_filters).rewrite(html)
     end