Any project deploys as a container via Dockerfile.vercel

Patch Changes

• 09743c6: Support deploying any project as a container via a Dockerfile.vercel or Containerfile.vercel marker. A new experimental container framework preset detects these files and is listed first so it takes precedence over all other frameworks — a project that also looks like (e.g.) a Next.js app will deploy as a container when one of these markers is present. As an experimental framework it is gated behind VERCEL_USE_EXPERIMENTAL_FRAMEWORKS. The @vercel/container builder now recognizes the .vercel markers, auto-discovers them when its entrypoint is <detect>, and supports root (non-service) container deploys.
• 03fbb1c: Fix container service build output so requests reach the function. Container services now do a normal build, emitting the function at the natural index path inside the nested services/<name>/ output along with a catch-all route, instead of namespacing under _svc/<name>/index with no route to it. Previously a request to the service root never matched the function.