iWaitForAjaxToFinish provide some ways to configure wait time for Ajax call

[MBouzeboudja]

We do auto-test using behat on Drupal 8, some Ajax calls take a lot of time to finish (> 6s) like when we upload CSV file to create a content, it would be nice if we have the possibility to configure the wait time of the iWaitForAjax function in order to increase or decrease it when we need.
We can have this time wait configuration in behat.yml for example.

We suggest also to add "attach" to afterJavascriptStep because in drupal we have some attach witch generate Ajax calls.

```

$text = $event->getStep()->getText();
if (preg_match('/(follow|press|click|submit|attach)/i', $text)) {
$this->iWaitForAjaxToFinish();

[stof]

there is no iWaitForAjax function in this repository