Allow specifying cron queue item lease time

Problem/Motivation

There's no way to specify a different lease time for queue items than the lease time used for the whole queue. There's a bug in the Drupal Cron service currently which results in queue items always being reserved for only 1 second (see #3230541). Once this bug has been fixed, the cron-time specified for a queue should be used for total queue lease times and queue item lease times.

This is, however, less than ideal since there are cases where a developer may want to reserve queue items for longer than the over-all queue. For example, if someone had a queue worker which might process an item for up to 5 minutes, but didn't want to continue picking up new items after 3 minutes.

Proposed resolution

Separate queue worker annotations should be used for for a queue's time-limit and for the lease time for queue items.
A new "lease_time" annotation could be created which allows for specifying queue item lease times.

Use of the new annotation would look something like this:

<?php

namespace Drupal\slow_queue\Plugin\QueueWorker;

use Drupal\Core\Queue\QueueWorkerBase;

/**
 * Sleep for 5 minutes and then log a message to watchdog.
 *
 * @QueueWorker(
 *   id = "slow_queue",
 *   title = @Translation("This queue worker processes items slowly and logs a message in watchdog when it's finished"),
 *   cron = {
 *     "time" = 30,
 *     "lease_time"=60
 *   }
 * )
 */
class SlowQueueWorker extends QueueWorkerBase {

  /**
   * {@inheritdoc}
   */
  public function processItem($item) {
    \Drupal::logger('slow_queue')->notice('Starting: ' . $data);
    sleep(60);
    \Drupal::logger('slow_queue')->notice('Done: ' . $item);
  }

}