[Task] Update Merlin Schema to include inputs, outputs, other metadata

[EvenOldridge]

Metadata schema updated to include:

• Input Schema
• Output Schema
• Data distributions?
• Prediction distributions?

[nv-alaiacano]

Meeting notes (not super complete): https://docs.google.com/document/d/1k_QJ063LH0YIJ_wPVzwjFzTQXek0UtXXtmErj_kqrOY/edit#

[karlhigley]

I don't think this task is about changing the existing schema format; it's more about creating a format for capturing a broader set of metadata (including but not limited to schema information), right?