Parameter and bug fixes in Role Assignment commands

[shuagarw]

Azure-powershell RoleAssignment command fixes

• Use GetObjectsByObjectId to optimize graph calls while converting RoleAssignments to PS objects.
• Fix parameter sets in New, Get and Remove RoleAssignments and api calls to use SignInName and remove upn and mail.
• Modify the output roleassignment object to add/remove fields.

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