Enable SkipGroup reusing dsc.exe

[SteveL-MSFT]

Summary of the new feature / enhancement

There are scenarios where you may want to reuse your config, but operations used with set would not apply to get or test. In those cases, you still want it defined in the config (instead of a separate config that is almost the same but different enough it becomes a process to keep the two in sync).

Proposed technical implementation details (optional)

The SkipGroup resource would accept a config doc with one additional property:

skipOn which would take a string array from possible values get, set, test, export

Alternatively, it could have a runOnlyOn accepting the same values. Not sure which is less confusing to users authoring and reading such a config.

The resource would emit an INFO (or maybe WARNING? although seems overkill, but more likely seen) messages on skipped resources.

This resource would not be part of the base DSC v3 package and needs to be installed separately,

[SteveL-MSFT]

With change in behavior for #302 (comment) we no longer need this for now