added possibility to specify task_key when creating a task programmatically

[lexsmil]

<?php
// Load the Scheduler service class
$path = $modx->getOption('scheduler.core_path', null, $modx->getOption('core_path') . 'components/scheduler/');
$scheduler = $modx->getService('scheduler', 'Scheduler', $path . 'model/scheduler/');
if (!($scheduler instanceof Scheduler)) {
    return 'Oops, could not get Scheduler service.';
}

/**
 * Get the task with reference "dosomething" in the "mycmp" namespace.
 * This task should have been added earlier via a build or the component.
 */
$task = $scheduler->getTask('mycmp', 'dosomething');
if ($task instanceof sTask) {
    // Schedule a run in 10 minutes from now
    // We're passing along an array of data; in this case a client ID.
    $task->schedule('+10 minutes', array(
        'client' => 15
    ),
    'any task key' // new feature
);
}