Let's say you have a systemd system unit:
[Unit]
After=suspend.target hibernate.target hybrid-sleep.target suspend-then-hibernate.target
[Service]
Type=oneshot
ExecStart=<start-user-unit-here>
[Install]
WantedBy=suspend.target hibernate.target hybrid-sleep.target suspend-then-hibernate.target
How can one start a user unit from this system unit?