Endpoint Middleware

Describe the problem

I would like to propose a better model for endpoints middleware rather than the global hooks.

Current state: Today, we only have what appears to be one (1) hook src/hooks.ts that is run every time SvelteKit receives a request.

Issue: While this is ok for general things such as checking for authentication with a pathname
e.g., check_auth if pathname.startsWith('/admin'). The handle becomes quite large and unwieldy to check each pathname, etc.

Describe the proposed solution

Proposal: Permit the creation of one (1) hook per Endpoint in addition to the globally defined hook.

// src/routes/user.hook.ts 
// This file can be used to perform a logic for this endpoint only

export async function handle({event, resolve}) {
  const {method, body} = event.request;

  // get to the page if GET request
  if (method === 'GET') return resolve(event);
  
  try {
    await validate(body)
    return resolve(event)
  } catch (error) {
    return Response(JSON.stringify(e), {status: 422})
  }
}

The sequence for Sveltekit hooks would be as follows

src/hooks.ts -> src/{endpoint}.hook.{ts/js} -> src/{endpoint}.{ts/js} -> src/{endpoint}.svelte

This would provide a nice global hook with the additional benefits of a hook per endpoint.

Alternatives considered

Current implementation is as follows and is a terrible experience.

export async function handle({event, resolve}) {
  const route = event.url.pathname
  const {method, body} = event.request;

  switch (route) {
    case '/users':
      if (method === 'GET') return resolve(event);
      try {
        await validateUserBody(body)
        return resolve(event)
      } catch (error) {
        return Response(JSON.stringify(e), {status: 422})
      }
      break;

    case '/notes':
      if (method === 'GET') return resolve(event);
      try {
        await validateNotesBody(body)
        return resolve(event)
      } catch (error) {
        return Response(JSON.stringify(e), {status: 422})
      }
      break;

    .... other endpoints....
  }
}


### Importance

would make my life easier

### Additional Information

I think this feature would be nice to have too many of the developers that are using Sveltekit today.

Start with src/hooks.ts and compare the proposed src/{endpoint}.hook.{ts/js} files with the existing endpoint files. Trace how requests reach endpoints, then verify that a global hook and an endpoint-specific hook can run in the proposed order without requiring pathname-based branching.