Fix sending of workflow completed event

[mamidenn]

Describe the change
As described in #1097 a workflow that ends in an EndStep does not lead to the WorkflowCompleted LifeCycleEvent being published because DetermineNextExecutionTime returns too early.
This PR remedies that by sending the event also in case of an early return from DetermineNextExecutionTime.

Describe your implementation or design
Extracted publishing of WorkflowCompleted into a separate method and added a call to that function before the early return if workflow is completed.

Tests
Yes, added a failing unit test that is green after the implementation is changed.

Breaking change
No

Additional context

• This is a slightly cleaned up version of executor should publish if EndWorkflow() is set to determine end of workf… #1098 with the appropriate description to get this bug fixed.
• Fixes WorkflowExecutor is not sending LifeCycleEvents.WorkflowCompleted when Workflow is marked with IStepBuilder.EndWorkflow  #1097