Add support for running PowerShell scripts server side with the proxy account in Builder

Add an option to the "Run PowerShell Script Block" builder action to force it to execute using the proxy account server side. Currently this action runs on the remote endpoint but it would open up new automation scenarios to have this able to run server side using a known account that can be delegated permissions to things. This would allow you to take actions on endpoints then trigger something in an external system like ServiceNow using an API call via PowerShell. If it let you specify the run as credentials along with the option of running server side it would be even better.