fix(error): Improve error message on snapshot creation (#655)

# Description

## Checklist
(For exoscale contributors)

* [ ] Changelog updated (under *Unreleased* block)
* [ ] Testing

## Testing

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Describe the tests you did
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cmd/instance_snapshot_create.go

@@ -46,6 +46,9 @@ func (c *instanceSnapshotCreateCmd) cmdRun(_ *cobra.Command, _ []string) error {
 
 	instance, err := globalstate.EgoscaleClient.FindInstance(ctx, c.Zone, c.Instance)
 	if err != nil {
+		if errors.Is(err, exoapi.ErrNotFound) {
+			return fmt.Errorf("resource not found in zone %q", c.Zone)
+		}
 		return err
 	}