Until a few months ago this worked: https://maps.google.com/maps?q=http://www.jcea.es/pics/italia2015/italia2015.kmz
It is NOT working anymore.
I know that I can login in Google maps, create a custom map and upload a KML file (if it has less than 2.000 points, my KML files are far bigger). But I don't want to upload a KML file, I want a map I can overlay a KML hosted in my HTTP/HTTPS server.
In fact I rather prefer to use something like OpenStreetMap instead of Google, but I don't know any service I could use.