Create a surrogate key snippet

Create a snippet following the [template contribution guide](https://github.com/cloudflare/workers-docs/blob/master/content/templates/CONTRIBUTING.md) for surrogate keys

Make sure to [migrate](https://github.com/cloudflare/workers-docs/blob/master/CONTRIBUTING.md#do-you-want-to-migrate-archived-documentation-to-the-new-docs) the [old recipe](https://developers.cloudflare.com/workers/archive/recipes/vcl-conversion/controlling-the-cache#setting-surrogate-keys-cache-tags).

More reference :
https://gist.github.com/victoriabernard92/ac70d59e8ea8bc3238b98c64a659198d