Add tabled

• Use yarn to add tabled dependency, instead of composer, as it is mandatory.
• Use corepack to pin dependency manager to yarn version.
• Add editorconfig file.
• Attach tabled to all pages---this is sub-optimal, but I am struggling to find a hook that would trigger when only certain CKEditor markup was present.
• Initialize tabled for all tables---this is sub-optimal, as it is unexpected for the library to attach to tables not created via the plugin. I am struggling to find a way to add a class to tables created in CKEditor 5.