feat: add CSRF allowedOrigins bypass list

[khromov]

Adds csrf.allowedOrigins config to whitelist trusted domains that can submit forms to your app.

Problem

Certain payment providers (and possibly auth services) redirect users back with form submissions that get blocked by CSRF protection. Previously you had to disable CSRF entirely or handle these outside SvelteKit. This is a fairly common Example thread

Solution

  export default {
    kit: {
      csrf: {
        checkOrigin: true,
        allowedOrigins: ['https://checkout.stripe.com', 'https://accounts.google.com']
      }
    }
  }

---

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[changeset-bot]

🦋 Changeset detected

Latest commit: 2cddffd

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@sveltejs/kit	Patch

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[svelte-docs-bot]

Preview: https://svelte-dev-git-preview-kit-14021-svelte.vercel.app/