If you want to use a KML map layer as described here you can host the kml file on Google Drive.
Just right-click on it and choose SHARE. Then click on ADVANCED and copy the link.
Paste this link here to get the Export Link:
Copy this Export Link and paste it in your column definition under “Optional Url for KML File”.
The kml file does not to be public. It can be private.
One thing I noticed: It will not work with https:// but only with http://