When using New-SdnMuxCertificate, it fails if FabricDetails not provided

[arudell]

Describe the bug
The function expects FabricDetails, which does not provide a lot of details on exactly this should be.

Description of fix
Should either define a class type around FabricDetails to be the $SdnDiagnostics.EnvironmentInfo array we generate, and/or make the field optional if do not need to export to rest of infra.