Outdated dependency on Metric for Product and Backend Methods in API Docs

Methods defined on Product or Backend trigger only Hits metric (as stated in Methods description: "Method calls trigger the built-in Hits-metric"). Which means that their dependency on other metric was depreciated (when APIAP was implemented).

metric_id field is mandatory for Product Method and Backend Method API Docs endpoints (List, Create, Read, Update, and Delete). 

The endpoints work correctly, but the user is required to always fill in the same metric_id (id of build-in metric Hits).