Includes the machine model in the body response

Adds custom_attributes[] — the machine model's typed custom-field definitions (key, type, config, translations, …) — to the included machine model, so the device's custom_attribute_values can be rendered with their labels, types and enum options. Requires include_machine_model: without it there is no machine model in the response to carry them.

Includes missing_custom_attributes[]: the recommended custom attributes of the device's model that are currently empty on this device. Must be true to take effect.