[prometheus-to-sd] Support for prometheus /federate endpoint

I'm interested in scarping metrics of the prometheus /federate endpoint. In order to do so I need to be able to configure the scape endpoint as well as supply some match expressions.

Thus I would like to extend the source URI by a metrics path and add the match parameter. Something like:
source=prometheus:http://localhost:9090/federate?match[]={job="prometheus"}&match[]={name=~"job:.*"}