AADGroupEligibilitySchedule should not use DisplayName as key

[mpoulson]

@sandrola and @NikCharlebois the Resource AADGroupEligibilitySchedule uses DisplayName as Key. This is different than AADGroupEligibilitySchedule which uses UPN or group name. Display Name is not a unique value and is not the best option.

I propose given AADGroupEligibilitySchedule was broken until my current changes that we also take the opportunity to refactor how it work.

My recommendation

1. Follow same model as AADGroupEligibilitySchedule to allow User (UPN), Group (Group Name) as Principal
2. Allow setting justification with the entry

Separately, I hope we can add PIM-Group Settings as a future resource type.