feat: patch fetch with tracing

[xplosunn]

Patches 'fetch' with tracing.

When running tests I found out that sometimes the patching was applied multiple times. Not sure if it's specific to testing or something that can also happen in production code, so I added a "patched" variable to track it.

[jonbretman]

I don't think this will be hugely useful as it won't track the full lifecycle of the request. There is some otel instrumentation for fetch which is intended for web-use but maybe is worth trying? https://github.com/open-telemetry/opentelemetry-js/tree/main/experimental/packages/opentelemetry-instrumentation-fetch I can't see anything particularly web-specific.

If it doesn't "just work" then maybe we can port that file to be node compatible

[jonbretman]

Key things we want to capture:

• URL being requested
• HTTP method
• Response status
• Request time

[xplosunn]

@jonbretman that package unfortunately only works on the browser. I'll try to port it over.

[xplosunn]

@jonbretman here's what I tried:

1. Adding the global browser fields that library depends on. Somehow the spans were silently not finishing.
2. Copy that file (and related files) but drop the dependency on opentelemetry-sdk-trace-web. Turns out everything is built on top of that package, so there's no point.

So I ended up digging in the source code an copy-pasting the parts that seemed like things we want, including what you listed, apart from "Request time". The logic for that is a few hundred lines of code. It has a bunch of stuff for observing some events and filtering to get to the relevant times.

Is it worth bringing that over or is this an acceptable version for now?

[adaam2]

LGTM 🌈