Metrics endpoint has plural and singular mbeans/mbean

In the PuppetDB API most endpoints are plural in the sense that they look like /nodes/certname/facts/factname but the Metrics endpoint is different.

To get a list of all metrics /metrics/mbeans is queried whereas a single metric is queried as /metrics/mbean. This is inconstant with the rest of the API where querying for /nodes gives you all the nodes and /nodes/certname a single node, facts and resources behave similarly.