fixes NEXT-479
## content
This PR adds a `getTracer` API to Next.js that uses the `otel/api` under
the hood to provide Next.js level instrumentation through Open
Telemetry.
This also adds an example `with-opentelemetry` to demonstrate how it can
be used, assuming you have a collector.
This allows most notably to have `getServerSideProps` and `fetch` calls
inside Server Components traced.
## details
- we hide most internals spans, if you want to see all of them, use the
NEXT_OTEL_VERBOSE=1 env var
- if you want to use this, you'll need to rely on the
`config.experimental.instrumentationHook` config option to initialise
OTEL, like in the example
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [ ]
[e2e](https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs)
tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)
## Documentation / Examples
- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)
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