[FAB-10169] add support to retrieve metadata

Validation plugins need support to retrieve ledger metadata so that they
can handle state-based endorsements. This change set extends the state
dependency with the relevant functions.

Change-Id: I0a6f4ee2bce261a131c316b4410c2bc813c3c98e
Signed-off-by: Alessandro Sorniotti <ale.linux@sopit.net>

Author: ale-linux

core/handlers/validation/api/state/state.go

@@ -22,6 +22,12 @@ type State interface {
 	// The returned ResultsIterator contains results of type *KV which is defined in protos/ledger/queryresult.
 	GetStateRangeScanIterator(namespace string, startKey string, endKey string) (ResultsIterator, error)
 
+	// GetStateMetadata returns the metadata for given namespace and key
+	GetStateMetadata(namespace, key string) (map[string][]byte, error)
+
+	// GetPrivateDataMetadata gets the metadata of a private data item identified by a tuple <namespace, collection, key>
+	GetPrivateDataMetadata(namespace, collection, key string) (map[string][]byte, error)
+
 	// Done releases resources occupied by the State
 	Done()
 }