Add collectd integration for easy system-level metrics #4
Description
- option 1: make it a function of Metrics Agent - using existing (collectd-java integration](https://collectd.org/documentation/manpages/collectd-java.5.shtml)
- option 2: make it a function of Metrics Agent - using collectd-unixsock
- option 3: make it a separate runtime module using c++ client and metrics avro
For demonstration add disk and cpu stats to broker graphs.