Implement `prefixed` for schemas

[spl]

prefixed doesn't work for schemas yet. This is not intentional, it's a missing feature.

Originally posted by @matko in https://github.com/terminusdb/terminusdb/issues/775#issuecomment-972731515

[matko]

This is talking about the document get endpoint, which is able to return types and properties in either prefixed form (foo:bar, or just bar when it's in the @base or @schema (depending on context)) or expanded form.