Purging should happen async

[jasonbahl]

Problem

Currently, when WPGraphQL Smart Cache determines that there are queries to purge, it kicks off a foreach loop and purges them.

This is happening during a user session (typically when saving/publishing a post), causing slowdowns.

This screenshot was provided by a user showing their "publish/update" actions in the admin taking a while.

Proposal

I believe that instead of purging the caches immediately, we refactor this to happen async.

We determine which caches to purge and place them in a "queue", then send off a non-blocking HTTP request back to WordPress which would then work through that queue and purge the caches.

This will allow for users to publish/update content without having to wait for the purge action to complete.