Add dump command

Change-Id: If38d01ebb8788090f91a76daf6b7fc9add0320b7
diff --git a/src/netconf_access.hpp b/src/netconf_access.hpp
index 924b2c2..d9830bd 100644
--- a/src/netconf_access.hpp
+++ b/src/netconf_access.hpp
@@ -45,6 +45,8 @@
 
     std::shared_ptr<Schema> schema() override;
 
+    std::string dump(const DataFormat format) const override;
+
 private:
     std::vector<ListInstance> listInstances(const std::string& path) override;