docs: link the Cloudflare adapter for Workers (#78610)
Thanks for adding a link to the Cloudflare adapter.
This PR updates the link to the adapter to link the adapter based on
OpenNext which is our current recommended solution to deploy to
Cloudflare Workers.
(The existing link was to Next on Pages which was our former solution).
Co-authored-by: JJ Kasper <jj@jjsweb.site>
