chore(user-guide/testing): Add NodeJS Client Entry

Related-to: camunda/camunda-bpm-platform#4273

Author: psavidis

content/user-guide/ext-client/compatibility-matrix.md

@@ -48,6 +48,10 @@ Each version of Camunda 7 is bound to a specific version of the **External Task
     <td>7.21.x</td>
     <td>3.1.x</td>
   </tr>
+  <tr>
+    <td>7.22.x</td>
+    <td>3.1.x</td>
+  </tr>
 </table>
 
 Only these default combinations are recommended (and supported) by Camunda. Nevertheless, each version of the External