Add a default Ensure enum to PSDesiredStateConfiguration

[michaeltlombardi]

As an engineer developing and maintaining DSC Resources, I want to be able to leverage the most common pattern for ensurable state without having to redefine the Ensure enum in my own modules to reduce the reproduction of code and help me write idiomatic DSC Resources.

The current implementation suggestion for class-based DSC Resources requires every module with DSC Resources to redefine their own enum for Ensure, even if it uses the most common pattern (Present and Absent).

Proposal

I propose that the PSDesiredStateConfiguration module export a default ensure enum (possibly with a more unique name, like DscBasicEnsure) with the values Present and Absent, allowing DSC Resource developers to reuse that enum instead of redeclaring it. If an alternate implementation is required, the developer could still implement their own. Since all DSC Resources expect to be invoked via Invoke-DscResource (requiring PSDesiredStateConfiguration to be loaded), this should not be a blocker. Further, this implementation would be backwards compatible (I believe) and existing DSC Resources could opt into using it instead of their reimplementation.