Vendor `@fastify/otel` instrumentation

[andreiborza]

Description

We forked @fastify/otel before to downgrade its OpenTelemetry dependencies to v1 to match those of our SDKs. This came with issues on its own: #16281, #16300

Both pnpm and yarn v3 have issues with the way we specify the url to the fork, therefore we should switch strategy and vendor the instrumentation in.

Related to #16311

[github-actions]

A PR closing this issue has just been released 🚀

This issue was referenced by PR #16328, which was included in the 9.21.0 release.