Add vercel edge function example

[srikrsna-buf]

Add vercel edge function example.

This also adds client usage example, Vercel is claiming streaming support.

Using the fetch client from connect, the client for server steaming throws an error at the very end of the steam with: Invalid state: ReadableStream is locked. Which should be fixed in https://github.com/connectrpc/connect-es/pull/876

connect-web transport doesn't work on actual because of an unsupported fetch feature.

vercel dev doesn't work because of an issue in @vercel/node: https://github.com/vercel/vercel/pull/10701