Interact with Windows systems, part 2

[MikaelSmith]

#699 added the ability to mark entries that have their login shell set to powershell instead of a POSIX-compatible shell, but only external plugins could really use it. We need to define how to provide credentials and configuration, and add an implementation of WinRM that core plugins can use.

• Define how to configure WinRM details for an entry
  • Where is configuration stored? How is it set?
  • What configuration is needed?
• Add WinRM as a transport in Wash and use it for Windows targets in AWS/GCP.