AFAIK, you can also use the Skype for Business PS module for specific commands, for example meeting policies. However, it's not clear whether this works for aspects of voice. But to note, even in Skype for Business there wasn't the ability to do call forwarding through Powershell
The function you want is what Microsoft called SEFAUtil in Skype for Business, that is only available for Skype for Business Server, not for the online version and not for Teams. I'm suprised that there was no uservoice for this before so good that you started one @Christopher Hoard .