ws: Make ws_schema a generic update function
ws: Make ws_schema a generic update function

Previous implementation overwrites all device properties now they are
updated if the field already exists

CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source,CESARBR/knot-service-source