B-48400

Configure Metrics for off/on to stop collection Yammer Metrics Stuff

Basically, I've added a new attribute to the root element of the metrics.cfg.xml config file that allows a user to enable/disable metrics reporting. If the attribute is set, anytime the metrics service is requested, a null object is passed instead. This saves us the effort of checking if reporting is enabled/disabled in more than one place. This also prevents additional metrics related objects from being created.