Add systemd units for OpenHarmony 3.0

First pass for the OpenHarmony init services turned into systemd units.

Closes #47 (closed)

recipes-openharmony/openharmony/files/accountmgr.service

+[Unit]
+Description=OpenHarmony Account Manager service
+Requires=appspawn.service
+After=appspawn.service
+
+[Service]
+Type=exec
+# should run as system:system
+ExecStart=/usr/bin/sa_main /system/profile/accountmgr.xml
+
+[Install]
+WantedBy=multi-user.target