Add missing property to com.sun.star.graphic.MediaProperties service

An omission from commit 8484e52675
"tdf#117427 missing API for determining and loading linked graphic",
2018-05-12, that introduced it.

Change-Id: Ibf4c754931f813c5234daa5f7b7c907ed84efdef
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/172008
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
Tested-by: Jenkins

offapi/com/sun/star/graphic/MediaProperties.idl

@@ -101,6 +101,14 @@ published service MediaProperties
     appropriate filter module.
     */
     [optional, property] ::com::sun::star::beans::PropertyValues FilterData;
+
+    /** This property is only used for loading graphics
+
+        <p>Load the graphic as an external link</p>
+
+        @since LibreOffice 6.1
+    */
+    [optional, property] boolean LoadAsLink;
 };
 
 } ; } ; } ; } ;