Add mjModel.tendon_armature (in preparation, not yet implemented)

PiperOrigin-RevId: 743649968
Change-Id: I48f8945923b0b32911ea18677af8939dce3c7789

Author: yuvaltassa

dm_control/mjcf/schema.xml

@@ -1858,6 +1858,7 @@
             <attribute name="springlength" type="array" array_type="float" array_size="2"/>
             <attribute name="stiffness" type="float"/>
             <attribute name="damping" type="float"/>
+            <attribute name="armature" type="float"/>
             <attribute name="user" type="array" array_type="float"/>
           </attributes>
           <children>
@@ -1890,6 +1891,7 @@
             <attribute name="frictionloss" type="float"/>
             <attribute name="stiffness" type="float"/>
             <attribute name="damping" type="float"/>
+            <attribute name="armature" type="float"/>
             <attribute name="user" type="array" array_type="float"/>
             <attribute name="solreflimit" type="array" array_type="float" array_size="2"/>
             <attribute name="solimplimit" type="array" array_type="float" array_size="5"/>