Add state merkle tree root and/or ledger height to read request responses

[gennadylaventman]

When doing a read query, the result may serve as a proof that can be given to a third party. When proving that a datum exists, the result currently contains only the <key, value, version, meta> of the datum. It is useful to include a field that captures the point in time when this was true in relation to the ledger. That can be captured by two pieces of data the current height of the ledger, and/or the state merkle tree root.