Given an array of integers and a target integer, write a method groupSumWithNum to determine if it is possible to choose
a group of integers from the array such that the group sums to the given target. An additional
constraint is that the summation must include the integer must_have if it is
present in the array.
Select the element at each step of the recursion by incrementing the start_index and keep subtracting it from the target to reach the base condition. The key here is to include the must_have integer as part of the target.