images command should display image Created time or N/A if not available

Signed-off-by: Nicolas De Loof <nicolas.deloof@gmail.com>

pkg/api/api.go

@@ -603,7 +603,7 @@ type ImageSummary struct {
 	Tag         string
 	Platform    platforms.Platform
 	Size        int64
-	Created     time.Time
+	Created     *time.Time
 	LastTagTime time.Time
 }