Pyroscope: Provide an example for ebpf sidecar collection

[simonswine]

This shows how Alloy can be used to collect profiles as a sidecar. I am not too sure if this is something we should advertise too heavily, but valuable if you would only like to collect a very specific workloads, that is supported by eBPF.

Maybe we also want to have something like pyroscope exec was for this usecase.

The test workload launches some short-lived sub processes of varying length, the problem is that collection requires to have a quite low discovery.process.refresh_interval

[simonswine]

@korniltsev if you got a moment, would like to understand how you feel about this