- Add device_role field to Device struct in client
- Add device_role and device_role_source to DeviceResourceModel
- Add schema attributes for device_role (optional/computed) and device_role_source (computed)
- Handle device_role in Create, Read, and Update operations
- Valid device_role values: server, switch, router, access_point, backhaul, other
- device_role_source automatically set to 'manual' by API when device_role is provided