--output-format should have a `as-json-array` option

[SteveL-MSFT]

Summary of the new feature / enhancement

This is specific to dsc resource list and dsc extension list which returns JSONLines where each line is a JSON object. However, there's been some requests to have those commands emit a single JSON object that can be deserialized at once. To not break existing usage, we can add a as-json-array to the supported values. However, this option doesn't make sense for other cases like config and resource which returns a single JSON object.

Proposed technical implementation details (optional)

In the code, we'd have a separate enum for dsc resource/extension list with as-json-array

[SteveL-MSFT]

dsc resource get --all --output-format json-array was added, so this should just be json-array