Add support for using queues for sending submissions to CiviCRM

I am not sure whether I understand this issue correctly and that is because the CiviCRM McRestFace (CMRF) Framwork already provides queuing. To queue a call for later execution one can set to be scheduled.

I also believe that the CiviCRM McRestFace has the ability to retry failed calls however I am not sure whether that is fully functional.

To explain a bit more about the CiviCRM McRestFace Framework. It is a platform agnostic approach for calling the CiviCRM Api. Implementations exists for at least wordpress, Drupal 7 and Drupal 8/9/10/11.

The platform agnostic part is called CMRF Abstract Core and can be found here: https://github.com/CiviMRF/CMRF_Abstract_Core

The Drupal 8/9/10/11 implementation (inlcuding configuration screens) for the Abstract Core is called cmrf_core and can be found here: https://www.drupal.org/project/cmrf_core →

As discussed in the call:

• calls are stored in the civicrm_api_call table
• calls can be scheduled to be executed at a later time
• calls can be retried N times after failing

This abstract functionality is provided by the cmrf_abstract_core package. Let's try to keep using Drupal queues, but use the civicrm_api_call table as storage backend. If that turns out to be too difficult we can still consider dropping Drupal queues completely, or to use the current implementation that uses the Drupal queue storage.

An advantage of using Drupal's queue backend is that you can e.g. use Redis → instead of a database table. We're not currently using that though, so not super important.

An advantage of using CMRF's queue backend is that it integrates with the /admin/reports/cmrfcalls overview, which is a useful interface for the client.

I'll have another look at this MR soon.