WIP: HTTP client request tracking

[grcevski]

This PR introduces nested span tracking, although it's not perfect as it doesn't deal with async HTTP client requests. Essentially we instrument the HTTP client and make client spans, but we also track the parent server request scope.

I still need to do a lot of test writing and validation.

[codecov-commenter]

Codecov Report

Merging #85 (039a424) into main (2ceff1a) will decrease coverage by 0.42%.
The diff coverage is 54.63%.

@@            Coverage Diff             @@
##             main      #85      +/-   ##
==========================================
- Coverage   46.58%   46.17%   -0.42%     
==========================================
  Files          15       15              
  Lines        1172     1241      +69     
==========================================
+ Hits          546      573      +27     
- Misses        577      615      +38     
- Partials       49       53       +4     

Flag	Coverage Δ
unittests	46.17% <54.63%> (-0.42%)	⬇️

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

Impacted Files	Coverage Δ
pkg/ebpf/nethttp/bpf_debug_bpfel_x86.go	0.00% <0.00%> (ø)
pkg/ebpf/nethttp/nethttp.go	0.00% <0.00%> (ø)
pkg/pipe/config.go	48.48% <ø> (ø)
pkg/transform/spanner.go	81.48% <50.00%> (-0.80%)	⬇️
pkg/export/otel/traces.go	63.29% <56.96%> (-10.19%)	⬇️
pkg/pipe/instrumenter.go	81.35% <100.00%> (+1.35%)	⬆️

[grcevski]

Code structure changed quite a bit. I'm going to close this PR and start from scratch.