add custom txn conflict error

datastore/memory/errors.go

@@ -15,5 +15,15 @@ import "github.com/sourcenetwork/defradb/errors"
 var (
 	ErrReadOnlyTxn  = errors.New("read only transaction")
 	ErrTxnDiscarded = errors.New("transaction discarded")
-	ErrTxnConflict  = errors.New("transaction conflict")
+	ErrTxnConflict  = txnConflictError{errors.New("transaction conflict")}
 )
+
+type txnConflictError struct {
+	error
+}
+
+// custom error formatting that is non idiomatic but matches the
+// Badger transaction conflict message
+func (e txnConflictError) Error() string {
+	return "Transaction Conflict. Please retry"
+}