Add equivalent inertia ellipsoid visualization.

PiperOrigin-RevId: 519154067
Change-Id: Idcab812137048d6aeb8a91adddaa628f73a7f5a3

Author: kevinzakka

dm_control/mjcf/schema.xml

@@ -123,6 +123,7 @@
             <attribute name="glow" type="float"/>
             <attribute name="offwidth" type="int"/>
             <attribute name="offheight" type="int"/>
+            <attribute name="ellipsoidinertia" type="keyword" valid_values="false true"/>
           </attributes>
         </element>
         <element name="quality">