Add support for executing RPCs

Creating a temporary YangAccess for RPC input means I need to somehow
give the right libyang schemas. For that reason I supply a callable
which is able to fetch the schema and create a YangAccess instance for
ProxyDatastore.

The ProxyDatastore class now has a simple mechanism for deciding whether
to use the normal datastore and the temporary based on a path prefix.

Change-Id: Ib455f53237598bc2620161a44fb89c48ddfeb6e3
diff --git a/src/interpreter.hpp b/src/interpreter.hpp
index 000cc21..0807c02 100644
--- a/src/interpreter.hpp
+++ b/src/interpreter.hpp
@@ -29,6 +29,9 @@
     void operator()(const copy_& copy) const;
     void operator()(const move_& move) const;
     void operator()(const dump_& dump) const;
+    void operator()(const rpc_& rpc) const;
+    void operator()(const exec_& exec) const;
+    void operator()(const cancel_& cancel) const;
 
 private:
     [[nodiscard]] std::string buildTypeInfo(const std::string& path) const;