Add hot config reload

Add configurable hot config file reload mechanism to support kube ConfigMap pyroscope.properties updates that dont trigger restart.

Linux inotify (upon which the jvm watch service virtualizes) has pitfalls, like inability to track NAS which are provided in modern clouds (like Amazon EFS NAS). I guess other OSs have push pitfalls, too. Also, some OSs dont support push, so the jvm polls internally. Thus, I would suggest pull model with 15m or so default interval configurable via --config-check-interval and a /reload real time endpoint.