Refine e2e tests

[pellared]

Based on my experience in https://github.com/open-telemetry/opentelemetry-dotnet-instrumentation (where I am a maintainer) I find testing against a "test fake collector" makes the tests more maintainable:

• spinning up a a httptest server or by setting up a gRPC server in tests is faster than running a real collector [image]
• you get more flexibility in assertion logic

Here you can find an example implementation and usage of a "test fake collector" in Go: https://github.com/signalfx/splunk-otel-go/blob/main/distro/otel_test.go

Originally posted by @pellared in https://github.com/open-telemetry/opentelemetry-go-instrumentation/pull/46#pullrequestreview-1359674606

CC @damemi

[pellared]

Removing from Beta project as I do not think it is a blocker.

[damemi]

From https://github.com/open-telemetry/opentelemetry-go-instrumentation/pull/738:

The bug in this PR can happen approximately once every 50-100 client spans (since page size is 4096 bytes and we write ~40 bytes per request in gRPC for example)

1-2% of the time isn't insignificant, but I don't think any of our tests are set up for that kind of scenario. Maybe as part of #93 we should update the tests to send more than one span (ideally enough to cross the page threshold).