Resolved "Selecting "Upcoming Iterations" value of 0 prevents current iteration from being created"

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What does this MR do and why?

Relates to #468674 (closed)

The code change allows iterations to be created automatically even if the number of iterations in advance is 0.

Additionally, a test case was added to ensure that the CreateIterationsWorker is called when various conditions of the iteration cadence fields are updated.

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