Apply GA4 tracking to flash alerts

Introduces the data_attributes required for `ga4-auto-tracker` to
only the flash alert component. This has been achieved by:

1. Passing `data_attributes` to `flash_message_component.html.erb`.
2. Adding a  `data_attributes` property to `Admin::FlashMessageComponent`
   (so it is available to all extending components).
3. Populating `data_attributes` in `Admin::FlashAlertComponent` with
   required properties.

app/components/admin/flash_alert_component.rb

@@ -2,4 +2,16 @@ class Admin::FlashAlertComponent < Admin::FlashMessageComponent
   def component_name
     "error_alert"
   end
+
+  def data_attributes
+    {
+      module: "ga4-auto-tracker",
+      "ga4-auto": {
+        event_name: "flash_message",
+        type: component_name,
+        text: message,
+        action: "error",
+      }.to_json,
+    }
+  end
 end

app/components/admin/flash_message_component.html.erb

@@ -1,5 +1,8 @@
 <%=
 content_tag(:div) do
-  render "govuk_publishing_components/components/#{component_name}", { message: }
+  render "govuk_publishing_components/components/#{component_name}", {
+    message: message,
+    data_attributes: data_attributes,
+  }
 end
 %>

app/components/admin/flash_message_component.rb

@@ -11,4 +11,6 @@ def message
       @message
     end
   end
+
+  def data_attributes; end
 end