Make SvelteKit `sentryHandle` request handler a factory function

[Lms24]

Right now, the sentryHandle function is just a plain request handler. This comes the disadvantage that we cannot pass arguments to configure it, if we ever wanted to allow customization of its behaviour. Therefore, we should convert it to a factory function that returns a handler:

// hooks.server.js

// old
export const handle = sequence(sentryHandle, /* other handlers */);

// new
export const handle = sequence(sentryHandle(), /* other handlers */)

// so that in the future we could do things like
export const handle = sequence(
  sentryHandle({ tracePageLoads: true, traceDataRequests: false }), 
  /* other handlers */
)

We'll do this right now to avoid legacy API before GA