Prior to this commit, as a matter of undocumented practice, we would
overwrite past experiments with upcoming experiments.
With this commit, we're leveraging a feature of the field_test gem:
declaring a winner. Instead of overwriting an experiment with the next
experiment, we're going to declare the expiring experiment's winner then
prepend to the ./config/field_test.yml the new experiment.
The [field_test/app/views/field_test/experiments/index.html.erb][1] then
uses logic to first render "active" experiments and "completed"
experiments. A "completed" experiment is one in which we've declared a
winner.
Closesforem/forem#17816
[1]:https://github.com/ankane/field_test/blob/master/app/views/field_test/experiments/index.html.erb
8fb98b9f30