Add error strategy shortcuts

The errorStrategy 'retry' implicitly terminates the execution when a task exceeds the max number of allowed retries.

There are use cases in which the user wants to ignore of finish the workflow execution. This is possible by using a dynamic error strategy (closure). However it would be useful to provide two new synthetic error strategies to simplifies the above use case, such as:

• retryThenIgnore: task execution is retried in case of error, if the errors exceed the maximum number allowed the task is ignored by applying the ignore error strategy.
• retryThenFinish: task execution is retried in case of error, if the errors exceed the maximum number allowed the execution is stopped by applying the finish error strategy.