Create documentation on how to use ably-js with Vercel for both frontend and serverless functions, including using Vercel Edge runtime

[VeskeR]

1. create an article detailing the integration of ably-js with Vercel, and using Vercel Edge runtime. Update the Vercel websocket connections guide page to direct users to this specific article instead of solely redirecting to the Ably homepage.

This should include setup guidance, common caveats, and how to deal with them (see https://github.com/ably/ably-js/issues/1735 for some of them), as well as use cases.

2. update the README in the ably-js repo to include short guidance on how to use it in Vercel serverless functions and with Vercel Edge runtime.

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