Provide a cache invalidation endpoint for static builds

[eric-burel]

Is your feature request related to a problem? Please describe.

vercel/next.js#21903
https://www.reddit.com/r/nextjs/comments/p37y5r/invalidate_cache_after_post_request/
vercel/next.js#10945
vercel/next.js#10721 (comment)
vercel/next.js#22384
https://stackoverflow.com/questions/68444505/how-to-clear-delete-cache-in-nextjs

Edit: See leerob comment: vercel/next.js#11552 (comment)

Describe the solution you'd like

• An API route that acts as a webhook to invalidate some statically rendered/ISR pages? Not sure if that works as API routes might live in a different volume.
• Implementing A possible strategy for cache purging vercel/next.js#22384 => needs a custom server
• Using a hidden param hack: change the hidden param value on demand (eg store it in redis or in the db), and rewrite to the URL with this param. When the param change, it force a new render.