Improve examples for formatting Y axis

Add an example for adding to an existing Y axis config without overriding it.

Author: hellomedia

src/Chartjs/doc/index.rst

@@ -185,6 +185,17 @@ custom Stimulus controller:
             console.log(event.detail.config);
 
             // For instance you can format Y axis
+            // Add a new scales config
+            event.detail.config.options.scales = {
+                y: {
+                    ticks: {
+                        callback: function (value, index, values) {
+                            /* ... */
+                        }
+                    }
+                }
+            };
+            // Add to an existing Y axis config
             event.detail.config.options.scales.y.ticks = {
                 callback: function (value, index, values) {
                     /* ... */