Separate code for different eBPF samplers

[mariomac]

Currently we track GRPC, Goroutines and HTTP in a single file. This will be a bit unmaintainable as long as we keep growing in languages and libraries.

Currently, the instrumenter looks for the offsets of all the instrumentable functions (GRPC, goroutine queuing, HTTP...) and returns a map with all the found offsets, which are passed to a single eBPF loader.

I'd suggest to do the following architectural change:

The instrumenter should look for all the instrumentable functions, but should return multiple maps that would trigger different parts of the code selectively (for example, if only net/http Serve functions are found, load the BPF code of the HTTP tracer and the BPF code for the Goroutine tracer).

This will require:

• splitting the go_nethttp.c code into go_grpc.c, go_server_common.c etc.... This will require multiple ebpf/... subpackages.
• Optionally, sharing ringbuffers when HTTP and GRPC are traced at the same time.
• Modifying the executable offsets inspector.