web: link fetch to page view span

[valerybugakov]

Context

Spans created by @opentelemetry/instrumentation-fetch always make independent traces, and the instrumentation doesn't provide an API for controlling span context.

This PR extends the default WebTracerProvider implementation to patch the behavior of the @opentelemetry/instrumentation-fetch tracer. Fetch spans created by the instrumentation when the window load span is recording are linked to it.

Test plan

Should be tested together with https://github.com/sourcegraph/sourcegraph/pull/43994. See the test plan there (these PRs are stacked).

App preview:

• Web

Check out the client app preview documentation to learn more.

[sg-e2e-regression-test-bob]

Bundle size report 📦

Initial size	Total size	Async size	Modules
0.04% (+1.00 kb)	0.01% (+1.01 kb)	0.00% (+0.01 kb)	0.00% (0)

Look at the Statoscope report for a full comparison between the commits def5238 and 5773b39 or learn more.

Open explanation

• Initial size is the size of the initial bundle (the one that is loaded when you open the page)
• Total size is the size of the initial bundle + all the async loaded chunks
• Async size is the size of all the async loaded chunks
• Modules is the number of modules in the initial bundle

[sourcegraph-bot]

Codenotify: Notifying subscribers in OWNERS files for diff 2a70511...def5238.

Notify	File(s)
@sourcegraph/frontend-platform-devs	client/observability-client/src/instrumentations/fetch.ts client/observability-client/src/sdk/index.ts client/observability-client/src/sdk/tracer.ts