Warn on cases where there will be no results

[jaredlockhart]

If an experiment ends and the enrollment end date and the end date are the same, no results will ever be generated (since the obvservation period is 0 days). However Experimenter will still say Results expected <some date> which is not true, no results will be generated. We should catch cases where no results will ever be generated and notify the user of this.

┆Issue is synchronized with this Jira Task