This change introduces several things things:
1. Fixes the performance of the `/admin/abtests` page; instead of
rendering all of the experiment results, just render the overview.
2. Adjust the show page for an experiment to show the summary of
results.
3. Favor the existing "started_at" and "ended_at" attributes of
FieldTest (see https://github.com/ankane/field_test#config)
4. Update the field test experiments to include the `started_at` and
`ended_at` attributes.
5. Skip processing all non-active experiments in our conversion handler.
Why are there no tests? This is a page that is Admin only and is only
visible for reporting purposes. So, it's not quite worth writing tests
as you'd need lots of data. So we'll assume the logic from the upstream
[field_test gem][1] is adequate.
Closesforem/forem#17869
[1]:https://github.com/ankane/field_test
234fd8b08d