feat: sidebar plugin config UI

src/libslic3r/Config.hpp

@@ -2228,6 +2228,8 @@ public:
         // Vector value, but edited as a single string.
         one_string,
         plugin_picker,
+        // Raw JSON string value, edited through a dialog behind a button rather than in the row.
+        plugin_config,
     };
 
 	// Identifier of this option. It is stored here so that it is accessible through the by_serialization_key_ordinal map.