Refactor reporter to use event tree

[nsavoire]

Store trace events in a tree (similar to open-telemetry/opentelemetry-ebpf-profiler#528):
[ContainerId, Service] -> [Origin] (CPU,OffCPU,...) -> [Hash,Comm,Pid,Tid]

This makes emitting profile by service easier since events are already split by service.
This moves service determination from reporting time to trace event collection time, meaning that changes to process metadata (eg. exe name) will not be taken into account for already collected traces.

Also:

• Extract pprof generation code to its own package.
• Remove executablePath and apmServiceName from TraceAndMetaKey since they were not used.
• Use a unique dummy mapping for all interpreted frames.
• Use "kernel" as source file for kernel frames.
• Use following logic to determine process executable path in decreasing priority order:
  • Use /proc/<pid>/exe in addProcessMetadata if successful
  • Use TraceEventMeta.ExecutablePath if not empty
  • "kernel" if root frame is kernel
  • TraceAndMetaKey.Comm: since it's retrieved by eBPF it can be non empty even if TraceAndMetaKey.ProcessName is empty

[Gandem]

Nit: rename e to s since it's the service entity attributes

[nsavoire]

Done

[Gandem]

Thanks!