Add kubeconfig terms to glossary, update sidebar, make a v2.12 copy

shared-files/_glossary.md

@@ -159,6 +159,21 @@
     <p>
         <b>Related terms:</b> <i>RKE, RKE2</i>
     </p>
+    <dt>
+        Kubeconfig
+    </dt>
+    <p>
+        <b>Versions:</b> Rancher v2.12.0 and later
+    </p>
+    <dd>
+        A Rancher resource <code>kubeconfigs.ext.cattle.io<code> used to generate kubeconfigs.
+    </dd>
+    <dt>
+        kubeconfig
+    </dt>
+    <dd>
+        The kubeconfig file is used to configure access to Kubernetes when used in conjunction with <code>kubectl</code> or other clients. The kubeconfig contents can be generated by creating a Kubeconfig resource.
+    </dd>
 </dl>
 
 ## L