Tab autocomplete for Azure environment names should not be hard coded

[SamErde]

The list of environment names used for tab autocomplete in Connect-AzureADExporter is currently "hard coded." It would be better to dynamically base it on Azure's current list.

https://github.com/microsoft/azureadexporter/blob/b3f888856ae92ca18fd5d505666428b50d5d559f/src/Connect-AzureADExporter.ps1#L20

Since this module uses the Graph API, Get-MgEnvironment is probably the best way to pull the reference list.