Why this change?
This is a follow-up to 86b2e3a.
Basically, we want to allow people to select more than 1 group as well.
What does this change do?
1. Change `type: group` to `type: groups` and support `min` and `max`
validations for `type: groups`.
2. Fix the `<SchemaThemeSetting::Types::Groups>` component to support the
`min` and `max` validations and switch it to use the `<GroupChooser>` component
instead of the `<ComboBoxComponent>` component which previously only supported
selecting a single group.