Add whatif support to PS Adapter

[tgauth]

Summary of the new feature / enhancement

As a PS Adapter user I want to utilize whatif so that I can preview the impact - continuation of #70

Proposed technical implementation details (optional)

No response

[Gijsreyn]

@tgauth Hey Tess, I might be a bit eager on the work already on the winget-dsc repository, but I already took a shot to implement whatIf for Pip3Dsc. Knowing that this has not yet been developed in dsc.exe, I was curious what you think of the current branch implementation on: https://github.com/Gijsreyn/winget-dsc/blob/what-if-support/resources/PythonPip3Dsc/PythonPip3Dsc.psm1

You can see a method whatIf added. The executable that is being executed has the --dry-run option available. I'm capturing that output and add it to the _metaData property.

Do you mind having a look at it if you have time? Thanks in advance!