A stage that is capable of being cancelled.
A retryable task whose timeout is taken from the top level stage if that value has been overridden.
These are typically wait/monitor stages
TODO(rz): What even is the point of this interface?
A retryable task defines its backoff period (the period between delays) and its timeout (the total period of the task)
A discrete unit of work in a pipeline execution that does one thing and one thing only.
Represents the state of a TaskExecution .