Adds a child group to
parentGroup, or the repeater model if
null.
If
indexToInsert is provided the group is added at that position, otherwise it is added to the end.
The parent repeater group to insert into, or null if inserting a top-level group.(optional) An index in the groups array at which to insert the group. If not specified, the group will be added to the end.(optional) The metric set to use for the group data.A promise object that is resolved when the call is complete.
If successful, the new dundas.controls.RepeaterGroup is returned.