Add namespace in DeviceConfig to support ota teams's features

One sample usage is to toggle between server based or HAL based
implementation for resume on reboot.

Bug: 172780686
Test: adb shell device_config put ota server_based_ror_enabled true；
Check the value in system server code

Change-Id: Ia9d3cae788e9316850ce1fc417c12b5fc109b1a3