Add e2e testing

[xrmx]

Would be nice to run an e2e test checking that the code here is working with the the latest released elastic-opentelemetry (or even main?). The idea is to trace a simple example with opentelemetry-instrument and parse its output with jq and check that there is a span. We can probably test against a local ollama with a tiny model (https://ollama.com/library/smollm:135m for 92mb) so that the time to download the model would be bearable.