Add documentation about dispatchRequestUsing

[HugoHeneault]

As seen in #1113 some users needing to run actions on resources would love to know about dispatchRequestUsing method override.

Adding something about it in documentation would help! :)

Some php code that could be used as an example:

<?php
class ResendCardEnrollmentEmail extends Action
{
    use InteractsWithQueue;
    use Queueable;

    protected function dispatchRequestUsing(ActionRequest $request, Response $response, ActionFields $fields): Response
    {
        $ids = $request->get('resources');

        throw_if(empty($ids), 'No resource selected.', ResponseHttp::HTTP_UNPROCESSABLE_ENTITY);

        $cardQuery = Card::query();

        // if all cards are selected, nova returns 'all' instead of an array of ids
        // so we only have to filter if it's not 'all'
        if ($ids !== 'all') {
            $cardQuery->whereIn('ulid', $ids);
        }

        // do not load each model individually, just get the ids
        $cardsIdsToDispatch = $cardQuery->pluck('ulid');

        // Do the heavy work now

        // Then return response
        return $response->successful(ActionResponse::message($cardsIdsToDispatch->count() . ' resources handled');
   }
}