[Feature] Create a global vercel like context

[conico974]

We should create a global request context with AsyncLocalStorage that would look like the vercel request context and would allow us to hook into next/after easily.
We already have a global.__als, but it should be on every function and should cover the middleware as well

It could also allow people to access stuff like headers or cookies even in ISR/SSG

This would also allow us to provide a @vercel/request-context for libs that rely on this to detect if next is running in serverless (This should probably be optional since it could break some lib)