pprof

While setting up Parca for prometheus' prombench, I had to configure all the profiling configs, because we use a prefix.

Since the prefix is common to all, it would be useful to be able to provide the prefix.

instead of:

    profiling_config:                                                      
      pprof_config:
       memory_total:        
               enabled: true         

The duration in a pprof profile is supposed to be the real duration, instead of the intended duration, so parca-agent should be setting the duration that capturing the profile actually took instead of the configured interval.

https://github.com/parca-dev/parca-agent/blob/80e9cb0df9ae987900b85f8e41150af7ade275cb/pkg/profiler/profiler.go#L556