expand filters to be able to exclude any subgroup(s)

[JGreenlee]

We had a single checkbox to exclude test users, which worked fine for that purpose. But for programs with multiple subgroups we want to be able to filter by any of the subgroups

I modified this into a multi dropdown which has all subgroups from the config (or just 'test' if the config doesn't define subgroups)

I also made the default value reflect metrics.include_test_users from the config.

[JGreenlee]

Here is what the multi dropdown looks like