Vendor `@fastify/otel`

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Vendor in @fastify/otel into the SDK.

Follow this process:

1. Vendor the instrumentation as-is, with as little changes as possible.
2. Make sure each vendored file contains the licence on top.
3. Generally follow this folder layout:
   • src/integrations/tracing/fastify/index.ts for the Sentry integration
   • src/integrations/tracing/fastify/vendored/xxx for vendored files
4. Vendor in sub-dependencies of the instrumentation as much as possible, including types. Avoid adding runtime dependencies to the SDK.
5. Disable eslint for the files if necessary in the initial PR, and fix those in a follow-up.
6. In a follow-up PR, adapt or streamline the instrumentation to SDK needs, removing parts that are not needed.
7. Finally, rewrite integrations to not depend on @opentelemetry/instrumentation but implement an internal base.

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JS-2085