Publish lifecycle events of workflow and task to a particular topic

[Ouriel]

To be able to store and use the differents events for analytics purpose, it will be great if the a subset of start, completion, cancellation or failure of workflow and task in a specific topic. Use-case:

• build analytics dashboard relative to lifecycle of task and workflow using tags or metadata.

[geomagilles]

Note: currently there are no events such as TaskCompleted, TaskCanceled, WorkflowCompleted, WorkflowCanceled(it's not needed by the engine). Providing those events will be useful for analytics purposes when introspecting the topics. Btw the dashboard will need them also

[geomagilles]

Completed with 0.13.0