[webinterface] update copyright year

internal/server/web/partials/footer.mustache

 <div class="footer">
     <div style="text-align: center;">
-        <small style="color: #808080;">© 2022 KIT</small>
+        <small style="color: #808080;">© 2023 KIT</small>
         <small style="margin-left: 20px;"><a href="/privacy">Privacy</a></small>
         <small style="margin-left: 20px;"><a href="https://mytoken-docs.data.kit.edu" target="_blank"
                                              rel="noopener noreferrer">Documentation</a></small>