Might be used when tracker is behind reverse proxy and one of provided
addresses in `real_ip_header` is private/local address.
Additional changes:
* check if provided address is not multicast/broadcast
* configure `http.Server.ReadHeaderTimeout` with `http.ReadTimeout` to mitigate Slowloris
* update dependencies
* minor docs fixes
This change:
- renames pkg/prometheus into pkg/metrics
- renames the prometheus_addr config to metrics_addr
- adds pprof endpoints to the metrics server
- removes profile/trace cli flags
- adds endpoints for profiling to the metrics server