Support profile public key injection

[dvianello]

In the GCP deployment there's no support for profile_public_key to inject the user's key in the VM, as it apparently relies on GCP own key propagation mechanisms.

Keys can be injected directly in the VM like this:

metadata {
    block-project-ssh-keys = "True"
    sshKeys = "centos:${file("${var.portal_public_key_path}")}"
}

We also might need to stop the google-accounts-daemon on the VM to prevent it to override the key.