🐛 gcp compute instances should be labelled as platform instance not i…

…mage (#1591)

also, i didn't touch the logic for this part right now, but why are we
entirely skipping windows instances, like not discovering them at all?
@preslavgerchev @imilchev does one of you know?
```
		if disksContainWindows(i.Disks) {
			log.Debug().Msgf("skipping windows instance %s", i.Name)
			continue
		}
```

motor/discovery/gcp/mql_asset_objects.go

@@ -106,7 +106,7 @@ func computeInstances(m *MqlDiscovery, project string, tc *providers.Config, sfn
  name: i.Name,
  id: i.Id,
  service: "compute",
- objectType: "image",
+ objectType: "instance",
  },
  }, tc)
  a.State = mapInstanceStatus(i.Status)