It seems this changes the location of the configuration within the actual container
You may notice that the new public config folder is mapped to /config. Which is previously where Home Assistant's config folder was mapped if you added config to the map field.
This option is intended to replace the need for add-ons to map Home Assistant's config into their container. As such, an add-on cannot include both config and addon_config in the map field.
Going forward, if you do need to make Home Assistant's config available to your add-on, you should list homeassistant_config as a folder in the map field. Then Home Assistant's config folder will be mapped to /homeassistant within the container.