Add support for docker in rootless mode

[lelinhtinh]

Same #53, but in rootless mode.

The location of systemd configuration files are different when running Docker in rootless mode. When running in rootless mode, Docker is started as a user-mode systemd service, and uses files stored in each users’ home directory in ~/.config/systemd/user/docker.service.d/. In addition, systemctl must be executed without sudo and with the --user flag.
See https://docs.docker.com/config/daemon/systemd/#httphttps-proxy