Implement schema option for PsDscAdapter

[Gijsreyn]

PR Summary

This pull request adresses partially the option to call dsc resource schema -r <resourceName> for PowerShell adapters. If I'm not wrong, there is also an overarching issue but I couldn't find it. Pardon me on it.

There are other questions popping up with this pull request:

• How to define properties with types and description (proposal at 508)?
• Should definition metadata be included?
• How does the engine handle adapter resources to call schema executable through resource manifest?

PR Context

[SteveL-MSFT]

Please add some tests

[Gijsreyn]

Please add some tests

@SteveL-MSFT I added one test now with a hardcoded resource manifest. I'm struggling to find out the logic how dsc.exe handles adapter resources types. For now to not break the tests, i have hardcoded the type.

Do you mind helping me out and point me in the right direction? I would have expected the engine to call the dsc schema command on adapter resources directly.