RUCSS rows are not failed when they can't be added to the queue

[MathieuLamiot]

Context

In 3.15.3, the to-submit status was introduced for RUCSS table. When a row can't be sent to the SaaS (for any reasons, 401, unreachable API, etc...) the row remains in to-submit and is retried at the next cron interval. This can result in infinite loops for unauthorized users, or high CPU usage when a website can't reach the RUCSS API for instance, even if the feature is de-activated.

Expected behavior

• If a 'to-submit' row can't be sent to the SaaS, then it should be set to a failed status.
• To-submit jobs should not be processed if the RUCSS feature is not activated.

Acceptance Criteria

• No regressions with the nominal behavior (no error case).
• Force the failure of an API call from the plugin to the SaaS to register a job from a 'to-submit' row. The row should go to the status 'failed' with an error_message and error_code filled.
• Activate the RUCSS feature and purge the RUCSS table, wait for some rows to be added in 'to-submit'. Deactivate the feature. The jobs in to-submit must remain in that state forever. No API call to the SaaS should be performed.

Suggestion

• Add a check at the beginning of process_on_submit_jobs as in process_pending_jobs

  wp-rocket/inc/Engine/Optimization/RUCSS/Controller/UsedCSS.php

  Lines 476 to 480 in cb55163

  	if ( ! $this->is_enabled() ) {
  	$this->logger::debug( 'RUCSS: Stop processing cron iteration because option is disabled.' );
  	return;
  	}

• Instead of doing noting if can the send_api method did not return as expected, use the method make_status_failed:

  wp-rocket/inc/Engine/Optimization/RUCSS/Controller/UsedCSS.php

  Line 1013 in cb55163

  continue;

[CrochetFeve0251]

@MathieuLamiot adding a guarding at the entance of process_on_submit_jobs won't be useful at we already disabled it there if RUCSS is not enabled:

wp-rocket/inc/Engine/Optimization/RUCSS/Cron/Subscriber.php

Line 209 in cb55163

if (