New-vRAProject support for Viewers role

[GaryFlynn]

Steps to reproduce

Connect to vRA and attempt to create a new vRA project and include the -Viewers role

Expected behavior

Create a Project with the viewers role defined

Actual behavior

Creating the project fails as the -Viewers option is not defined. -Administrators and -Members are supported

Environment data

> $PSVersionTable
Name                           Value
----                           -----
PSVersion                      5.1.18362.752
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   10.0.18362.752
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1

> $vRAConnection
Server             : https://hostname.domain.com
Token              : <removed>
RefreshToken       : <removed>
APIVersion         : 2019-01-15
SignedCertificates : False
SslProtocol        : Default