Support Fastify v5

[Xhale1]

Problem Statement

Fastify v5 released recently, it'd be amazing to see Sentry v8 add support!

• Fastify v5 release on github
• Documentation on breaking changes
• Issue in the Open Telemetry repo

Solution Brainstorm

Most of the changes in v5 are removing deprecations, it seems little has changed beyond that. A comment in the linked OTEL issue had a good point that Fastify's new diagnostic channel support could be beneficial.

[mydea]

Thank you for opening this issue, we def. want to support this! We'll look into possibly contributing this upstream.