fastify-session should use onRequest hook

[QEDK]

Currently, the sessionStore emits a Fastify deprecation warning like this:
(node:12637) [FSTDEP006] FastifyDeprecation: You are decorating Request/Reply with a reference type. This reference is shared amongst all requests. Use onRequest hook instead. Property: sessionStore
In a future version this will result in fastify-session being incompatible. We should use the available onRequest hook to handle the session data.

[QEDK]

Dupe of #137