Add markAsFinished() method for overridability and make markJobAsFinished() protected

[stevebauman]

This PR adds the ability for developers to override the markAsFinished() and markJobAsFinished() methods on their extended Workflow model to perform other logic after a workflow has been marked finished, or one of its jobs:

Ventrue::useWorkflowModel(Workflow::class);

class Worfklow extends VentureWorkflow
{
    protected function markAsFinished(): void
    {
        parent::markAsFinished();

        // Other logic...
    }

    protected function markJobAsFinished(object $job): void
    {
        parent::markJobAsFinished($job);

        // Other logic...
    }
}

Let me know your thoughts! Thanks for your time 🙏

No hard feelings on closure ❤️

[ksassnowski]

Thanks!