Allow inviting users without a public profile to a group

[ChristopherThompson]

Please allow me to invite a user from another organization when i am provided their AGOL user name.  When inviting a user from another organization to a group, the user's name has to be publicly visible. Sometimes organizations have good and legitimate reasons for not allowing their users to be discoverable.  Not being able to collaborate with these users via group invites diminishes the utility of this capability.  

[GregGoldman1]

This will help with those "invisible users" that are impossible to find otherwise. I can see organizations that have valid security concerns regulating this, but in every case that I've encountered so far this has not been the case. Possibly having users designated public through defaults, then having the option to opt-out rather than having to opt-in as in now the case.