Alternative Sidebar Results availbility message for too-short observation window

[mikewilli]

If the observation window is less than 7 days, Jetstream can't compute weekly results and so none will be available for Experimenter. However, Experimenter currently just sees this as "no results yet" and provides the typical message about when results are expected. In this case, we should change the message to something like:

Experiment could not be analyzed: observation window too short.

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