Add lightweight observed request explorer

src/dashboard/dashboard.html

@@ -102,6 +102,9 @@
           <a class="button-link" href="../gvl-explorer/gvl-explorer.html">
             GVL-Explorer öffnen
           </a>
+          <a class="button-link" href="../request-explorer/request-explorer.html">
+            Request-Explorer öffnen
+          </a>
           <a class="button-link" href="../analysis-dashboard/analysis-dashboard.html">
             Request-/Empfänger-Analyse öffnen
           </a>