Fix missing gRPC/HTTP2 events

[grcevski]

This PR adds the ability to parse gRPC/HTTP2 events even if we missed the original connection event. Namely Beyla can start after the applications sends the PRI * HTTP/2.0 event and we will fail to register the http2 connection metadata. In this event Beyla will capture an unclassified TCP event.

We add a HTTP2/gRPC detector to the unclassified events and use a channel to add the missing metadata in the eBPF maps. Subsequent streams will see the metadata and correctly report the gRPC events.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 47.75161% with 244 lines in your changes are missing coverage. Please review.

Project coverage is 78.16%. Comparing base (b61e5c7) to head (189e687).
Report is 2 commits behind head on main.

Files	Patch %	Lines
pkg/internal/ebpf/bhpack/hpack.go	47.72%	95 Missing and 20 partials ⚠️
pkg/internal/ebpf/bhpack/huffman.go	40.83%	64 Missing and 7 partials ⚠️
pkg/internal/ebpf/common/http2grpc_transform.go	58.73%	15 Missing and 11 partials ⚠️
pkg/internal/ebpf/bhpack/tables.go	56.09%	16 Missing and 2 partials ⚠️
pkg/internal/ebpf/httpfltr/httpfltr.go	18.18%	8 Missing and 1 partial ⚠️
pkg/internal/ebpf/common/tcp_detect_transform.go	58.33%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #867      +/-   ##
==========================================
- Coverage   79.86%   78.16%   -1.70%     
==========================================
  Files         117      120       +3     
  Lines        8054     8486     +432     
==========================================
+ Hits         6432     6633     +201     
- Misses       1217     1410     +193     
- Partials      405      443      +38     

Flag	Coverage Δ
integration-test	56.00% <47.75%> (-0.37%)	⬇️
k8s-integration-test	61.91% <0.42%> (-3.24%)	⬇️
oats-test	34.15% <0.42%> (-1.74%)	⬇️
unittests	43.94% <0.00%> (-2.31%)	⬇️

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[mariomac]

Why copying the code instead of just doing:

import "golang.org/x/net/http2/hpack"

?

[grcevski]

I had to vendor it because it was failing on unknown fields. We want to ignore the unknown so that we can continue parsing until we find :method and :path.

[grcevski]

The test for these missing metrics is involved, so I'm going to split this work in another PR.