openharmony-standard_3.0: add user, run system services as system user

OpenHarmony init system, is responsible for creation of some directories, handling 
permissions and running services with appropriate UIDs/GIDs. Currently in 
meta-openharmony we have everything run as root, which causes some issues.

Adding system user with UID 1000. 
Run system services as system user.

Signed-off-by: Francesco Pham <francesco.pham@huawei.com>