Returns Cloud presets and unregistered camera slots.

Cloud preset (source: cloud)
Registered in Lumana Cloud. It has a Cloud ID, name, status and metadata. Its presetToken
identifies the numbered slot on the camera.

Native preset (source: native)
Exists on the camera but is not registered in Lumana Cloud. Its ID and name are null; its status is
UNREGISTERED.

Use source to distinguish the two kinds and register a native item before managing it as a Cloud preset.

If camera discovery fails, the endpoint still returns Cloud presets with HTTP 200. Therefore, an absent
native item does not prove that the corresponding camera slot is free.