add support for mermaid diagram to markdown editor

packages/node_modules/node-red/settings.js

@@ -422,7 +422,16 @@ module.exports = {
                 //fontFamily: "Cascadia Code, Fira Code, Consolas, 'Courier New', monospace",
                 //fontLigatures: true,
             }
-        }
+        },
+
+        markdownEditor: {
+            mermaid: {
+                /** enable or disable mermaid diagram in markdown document
+                 */
+                enabled: true
+            }
+        },
+        
     },
 
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