[Fastify] Pass all spans to requestHook

[mydea]

In the fastify instrumentation, only request_handler spans are passed to requestHook. This means there is no (easy) way to customize the middleware spans the instrumentation emits. This is different than e.g. in the express instrumentation, where all spans are passed to the requestHook. I think it would make sense to align this and also pass all spans to requestHook in fastify.

If this is OK, I could prepare a PR to change this?