feat(vercel): allow external redirects

[wotschofsky]

This PR was originally opened on the main Astro repo: withastro/astro#11422

Changes

Before:

Redirects with schema defined in astro.config.mjs were converted into paths on the same site: https://google.com -> /https://google.com

After:

External redirects are detected and don't have the project base path prepended.

Testing

The output (esp. .vercel/output/config.json) of building a project with the updated integration was manually inspected.

A test was added

Docs

The Astro docs generally state that supporting external links configured through astro.config.mjs isn't a goal. While the Cloudflare adapter already supports external redirects, the Vercel adapter handled external redirects differently so far. Therefore this could potentially be considered a breaking change.

[changeset-bot]

🦋 Changeset detected

Latest commit: 6c06aba

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

This PR includes changesets to release 22 packages

Name	Type
@astrojs/vercel	Minor
@test/astro-vercel-basic	Patch
@test/astro-vercel-function-per-route	Patch
@test/astro-vercel-image	Patch
@test/vercel-isr	Patch
@test/vercel-max-duration	Patch
@test/vercel-edge-middleware-with-edge-file	Patch
@test/vercel-edge-middleware-without-edge-file	Patch
@test/astro-vercel-no-output	Patch
@test/astro-vercel-prerendered-error-pages	Patch
@test/astro-vercel-redirects-serverless	Patch
@test/astro-vercel-redirects	Patch
@test/vercel-server-islands	Patch
@test/astro-vercel-serverless-prerender	Patch
@test/astro-vercel-serverless-with-dynamic-routes	Patch
@test/astro-vercel-static-assets	Patch
@test/astro-vercel-static	Patch
@test/vercel-streaming	Patch
@test/astro-vercel-with-speed-insights-enabled-output-as-server	Patch
@test/astro-vercel-with-speed-insights-enabled-output-as-static	Patch
@test/astro-vercel-with-web-analytics-enabled-output-as-static	Patch
vercel-hosted-astro-project	Patch

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