Align SvelteKit auth tutorial with Next.js

# Improve documentation ## Link https://supabase.com/docs/guides/auth/server-side/sveltekit ## Describe the problem Right now the SvelteKit auth tutorial is very complicated. It treats the Supabase client like state, plus redundantly initializes it in hooks. As remote functions gain popularity, this will age poorly. ## Describe the improvement Treat the Supabase client the same way it's treated in Next.js - make wrappers around createBrowserClient and createServerClient, and use them whenever the Supabase client is needed. Alternatively, make one wrapper that automatically chooses based on `$app/environment`'s `browser` - something like this: ```js import { createServerClient, createBrowserClient } from "@supabase/ssr"; import { PUBLIC_SUPABASE_URL, PUBLIC_SUPABASE_PUBLISHABLE_DEFAULT_KEY } from "$env/static/public"; import { browser } from "$app/environment"; import { getRequestEvent } from "$app/server"; export const createClient = () => { if (browser) { return createBrowserClient(PUBLIC_SUPABASE_URL, PUBLIC_SUPABASE_PUBLISHABLE_DEFAULT_KEY); } else { const event = getRequestEvent(); return createServerClient(PUBLIC_SUPABASE_URL, PUBLIC_SUPABASE_PUBLISHABLE_DEFAULT_KEY, { cookies: { getAll: event.cookies.getAll, setAll: (cookiesToSet) => { for (const { name, value, options } of cookiesToSet) event.cookies.set(name, value, { ...options, path: "/" }); }, }, }); } }; ``` ## Additional context [Next.js guide](https://supabase.com/docs/guides/auth/server-side/nextjs)