Rename `version` field for `dsc resource *` commands to `required_version`

[michaeltlombardi]

Summary of the new feature / enhancement

As a DSC maintainer and DSC user
I want the CLI arguments for DSC to map explicitly to their actual behavior,
So that I can better understand how DSC will behave when contributing to the project or using DSC.

Currently, the dsc resource subcommands define the version field as Option<String>. More accurately to the actual behavior, these fields should be called required_version or version_req and map to Option<ResourceVersion>.

Proposed technical implementation details (optional)

Updating this code can be done in a backwards-compatible way by defining --version as an alias for --required-version (or --version-req).

This would also enable us to continue to leverage the "parse, don't validate" pattern for handling data types in DSC.