Config schema missing

Attaching patch for new version of module and interdiff, because initial patch doesn't help when using 1.3 version of this module.
Concerning above feedback, currently layout_builder module describes layout settings as layout_plugin.settings.[%parent.layout_id] and core doesn't provide any schema for additional property in layout_plugin.settings, so we have to make such override to cover all possible layouts.

Still needs work for #4