WooCommerce jobs eat up PHP workers unnecessarily

[rmccue]

If the background processing in Cavalcade has a minor blip, or jobs start to exceed typical times, Action Scheduler (WooCommerce's custom job processing) will skip over using cron and start using async HTTP requests. As this happens when the queue processing is starting to be slow, the async processing can also be slow.

Worse, because these are then routed to the web workers rather than Cavalcade, autoscaling of Cavalcade won't kick in correctly, and PHP workers will be used up unnecessarily causing the web containers to be misused.

We can tweak Action Scheduler's behaviour to ensure it always uses wp-cron, and then further optimise how it uses wp-cron to ensure efficient processing. This should improve AS performance as well as avoiding impacts on the web containers from backlogged queues.

See also, https://github.com/woocommerce/action-scheduler/blob/trunk/docs/perf.md

Acceptance criteria:

• When WooCommerce is activated, Action Scheduler does not spawn async HTTP requests to process jobs