Unfortunately Google's Container-Optimized OS image doesn't come with systemd-journal-upload, although it should be generally available after systemd version 216. (The current stable image ships with version 232.)
It's possible to build your own image, but I can't figure out how to include systemd-journal-upload.
Is it just a --enable-remote flag in file overlay-lakitu/sys-apps/systemd/systemd-232.ebuild maybe?