Add ability to filter metrics in DropwizardExports #573

We are migrating from dropwizard metrics to prometheus right now. We exported all old dropwizard metrics to prometheus and added all metrics to prometheus one by one. However, there is a problem – metric is added to prometheus is exported via DropwizardExports too, so, we see two similar metrics in output.

It will be great if we can filter metrics are exported to Dropwizard by standard MetricFilter mechanism.