Siteglide CLI - Syncing a file with empty metadata object, causes sync to silently fail

---
metadata:
---

Syncing a file like this appears to work, but checking GraphQL the sync is not successful and the update has not been applied. E.g. if previously there was metadata and you intended to delete it, the change would not be applied.

We should check yml validation and check a) that this is allowed b) that a validation error throws a sync error properly.