epbf: Propagate PID namespace to kernel space

[simonswine]

If the ebpf profiler is running on another namespace than the host PID namespace, then the PIDs that are selected by Grafana Agent are not matching up with the ones collected.

This will respect the PID namespace the original process is running under.

Fixes #3002 #1994

Note this is based on #2996

[CLAassistant]

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