Ensure Fastify instrumentation sends data expected for name and description inference

Right now, Fastify sends data that's largely divergent from other instrumentation:

* op: `hook.fastify` is not registered anywhere, meaning we don't go through the correct span description/name inference rule. I'd propose `function` or `function.fastify` as a replacement.
* It doesn't seem like `middleware` is the correct replacement since Fastify themselves don't refer to hooks as middleware. Middleware could be added via third party dependencies, in which case they should go through our express instrumentation.
* attributes: A [few attributes]() are not registered in sentry conventions and there'd be other, more established hooks that can replace them.

Start with packages/server-utils/src/integrations/tracing-channel/fastify/instrumentation.ts, especially the operation and attributes referenced in the issue. Compare Fastify's emitted data with Sentry conventions and other instrumentation to determine the appropriate inference inputs. Done means the instrumentation sends registered, consistent data for span name and description inference.

Vom Indexierungsmodell aus dem Issue-Text verfasst.