Unauthorized (invalid or non-existent) user could be invited to relevant Organization

[PavloPetrina]

STR

1. Create the Org
2. Invite the user with an invalid user id like "invalid@clients"

AR: Unauthorized user invited to relevant Organization > http://take.ms/uhV3X / http://take.ms/svlC1
ER: System ignores the request and doesn't save the unauthorized user in the relevant Organization

Note: there is a variety of indentity providers thus we need to choose which we're going to support