Enable default context items derived from `request`

[voxpelli]

Prerequisites

• [X] I have written a descriptive issue title
• [X] I have searched existing issues to ensure the feature has not already been requested

🚀 Feature Proposal

In #136 / #137 defaultStoreValues was allowed to be a factory, but no parameters was actually sent to it.

I would like it if it was sent the request instance as an argument.

Motivation

Sending request as an argument to the defaultStoreValues factory allows one to easily bootstrap the request context with values derived from the request, which is something I have been doing for eg a logging function.

I will do a PR.

Example

fastify.register(fastifyRequestContextPlugin, { 
  hook: 'preValidation',
  defaultStoreValues: () => ({
    log: request.log.child({ foo: 'bar }),
  }),
});