NETOBSERV-1103: optimize ebpf agent map memory and cpu usage (#140)

* Optimize ebpf agent map memory usage
- switch to use pointer to metric instead of metric
- manuall trigger GC after flow eviction complete

Signed-off-by: msherif1234 <mmahmoud@redhat.com>

* Fix memory and cpu scale issue work around in #133

following up on https://github.com/cilium/ebpf/issues/1063


it seems we have a way to fix resources issues

Signed-off-by: msherif1234 <mmahmoud@redhat.com>
(cherry picked from commit b9c9a035b25bd5b349071977aff0d7aebca40e75)

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Signed-off-by: msherif1234 <mmahmoud@redhat.com>