NETOBSERV-201: configure LogLevel and Sampling

[mariomac]

It replaces the "Verbose" binary config option by "LogLevel", to match other Netobserv components.

It also adds configurable sampling rate.

The best way to test sampling is to use grafana to count the number of processed packets.

In the following image you can see the packet count during 3 differentiated periods: no sampling (100% of packets processed), sampling==2 (50% of packets processed) and sampling == 4 (25% of packets processed).

[codecov-commenter]

Codecov Report

Merging #16 (e6e5cef) into main (e9b1d44) will decrease coverage by 0.07%.
The diff coverage is 20.00%.

@@            Coverage Diff             @@
##             main      #16      +/-   ##
==========================================
- Coverage   43.72%   43.64%   -0.08%     
==========================================
  Files           8        8              
  Lines         478      488      +10     
==========================================
+ Hits          209      213       +4     
- Misses        253      260       +7     
+ Partials       16       15       -1     

Flag	Coverage Δ
unittests	43.64% <20.00%> (-0.08%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/agent/config.go	70.73% <ø> (ø)
pkg/ebpf/tracer.go	3.59% <14.28%> (+0.40%)	⬆️
pkg/agent/agent.go	79.41% <100.00%> (ø)
pkg/exporter/grpc_proto.go	90.32% <0.00%> (+4.83%)	⬆️

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[jotak]

lgtm