Update open62541-config.cmake.in

Missing the open62541_TOOLS_DIR variable

tools/cmake/open62541-config.cmake.in

@@ -1,3 +1,5 @@
 @PACKAGE_INIT@
 
 include ("@PACKAGE_target_install_dest_name@")
+
+set (open62541_TOOLS_DIR @PACKAGE_open62541_tools_dir@ CACHE PATH "Path to the directory that contains the tooling of the stack")