what is value for install_url

[vmachacek]

when i want to add policy to policies.json with follows new standard, what is the install_url value? In other words where is the latest xpi installation file hosted?

so far i have something like this

{
    "policies": {
        "ExtensionSettings": {
            "{54e2eb33-18eb-46ad-a4e4-1329c29f6e17}": {
                "install_url": "???",
                "installation_mode": "force_installed"
            },
         ....
        }
    }
}