Update mermaid script initialization settings

Change mermaid initialization to start on load and use await for running.

Author: VinceFINET

docs/_layouts/default.html

@@ -13,11 +13,12 @@
     {% if page.mermaid %}
     <script src="https://cdn.jsdelivr.net/npm/mermaid@11.12.2/dist/mermaid.min.js"></script>
     <script>
-      document.addEventListener("DOMContentLoaded", function(event) { 
-        mermaid.initialize({ 
-          theme: 'forest',
-          querySelector: '.language-mermaid'         
-        });
+      mermaid.initialize({ 
+        theme: 'forest',
+        startOnLoad: false 
+      });
+      await mermaid.run({
+        querySelector: '.language-mermaid'
       });
     </script>
     {% endif %}