Support environment variables DSC Meta Configuration

[Gijsreyn]

Summary of the new feature / enhancement

With the initial batch completed in #574, I want to be able to use environment variables in the directories field. The current implementation in preview.12 doesn't support the following:

{
  "resourcePath": {
    "allowEnvOverride": true,
    "appendEnvPath": true,
    "directories": ["%SYSTEMDRIVE%\\CompanyResources"]
  },
  "tracing": {
    "level": "TRACE",
    "format": "Default",
    "allowOverride": true
  }
}

Proposed technical implementation details (optional)

No response