Issue #3580212: [Notifications] cron cleanup

Closes #3580212

• Adds automatic cleanup of stale and expired notifications via cron
• Stale processing notifications (older than 30 minutes) are purged and replaced with error notifications
• Expired notifications older than 30 days are deleted along with their associated read entries

Testing instructions

• Create a stale processing notification (31m old)

  ddev drush php-eval "                                                                                                                                                                       
    \$handler = \Drupal::service(\Drupal\canvas\CanvasNotificationHandler::class);
    \$handler->create([                                                                                                                                                                       
      'type' => 'processing',                               
      'title' => 'Stale sync',
      'message' => 'Syncing content...',
      'key' => 'test-stale',
      'timestamp' => (int)(microtime(TRUE) * 1000) - 1860000,
    ]);
  "

• Create an active processing notification

  ddev drush php-eval "                                                                                                                                                                       
    \$handler = \Drupal::service(\Drupal\canvas\CanvasNotificationHandler::class);
    \$handler->create([                                                                                                                                                                       
      'type' => 'processing',                               
      'title' => 'Recent sync',
      'message' => 'Still going...',                                                                                                                                                          
      'key' => 'test-recent',
    ]);                                                                                                                                                                                          
  "

• Create an expired notification (31 days old)

  ddev drush php-eval "
    \$handler = \Drupal::service(\Drupal\canvas\CanvasNotificationHandler::class);
    \$handler->create([
      'type' => 'info',
      'title' => 'Ancient notification',
      'message' => 'From a month ago',
      'key' => 'test-expired',
      'timestamp' => (int)(microtime(TRUE) * 1000) - 2678400000,                                                                                                                              
    ]);                                                                                                                                                                                                                                                                                                                                     
  "

• Verify all three were successfully created

  ddev drush sqlq "SELECT * FROM canvas_notification ORDER BY timestamp DESC;"

• Run cron

  ddev drush cron                                                                                                                                                                             

• Fetch notifications

  ddev drush sqlq "SELECT **id, type, title** FROM canvas_notification ORDER BY timestamp DESC;"                                                                                                  

• Verify that:
  • The stale processing notification is gone, replaced by an error with title "Operation timed out", message "Syncing content...", and the same key as the processing notification it replaced
  • The recent processing notification is still present and unchanged
  • The expired info notification is gone