[PoC] Cgroup runtime extension

[rogercoll]

Description:

Link to tracking Issue: #30289

Testing:

Documentation:

[rogercoll]

Manually tested with a modified version of the OpenTelemetry collector that exposes the internal runtime metrics: https://pkg.go.dev/runtime/metrics

Deployed with very limited cgroup resources:

        resources:
          requests:
            cpu: "50m"      # Minimal CPU request
            memory: "64Mi"  # Minimal memory request
          limits:
            cpu: "100m"     # Minimal CPU limit
            memory: "128Mi" # Minimal memory limit

Resulting runtime metrics:

# HELP go_gc_gomemlimit_bytes Go runtime memory limit configured by the user, otherwise math.MaxInt64. This value is set by the GOMEMLIMIT environment variable, and the runtime/debug.SetMemoryLimit function. Sourced from /gc/gomemlimit:bytes
# TYPE go_gc_gomemlimit_bytes gauge
go_gc_gomemlimit_bytes 1.20795955e+08

...
# HELP go_sched_gomaxprocs_threads The current runtime.GOMAXPROCS setting, or the number of operating system threads that can execute user-level Go code simultaneously. Sourced from /sched/gomaxprocs:threads
# TYPE go_sched_gomaxprocs_threads gauge
go_sched_gomaxprocs_threads 1