Add HAProxy monitoring dashboard features

- Introduced a new `dashboard` frontend in HAProxy configuration to serve a real-time monitoring dashboard.
- Added support for returning prebuilt `dashboard.html` for `/` or `/index.html` paths.
- Updated test cases and expected outputs to accommodate the new frontend.

src/templates/haproxy.cfg.j2

@@ -91,6 +91,14 @@ frontend stats
 backend srv_stats
     mode http
     server Local 127.0.0.1:{{ data_stats["port"] | default(1936) }}
+
+frontend dashboard
+    bind *:{{ (data_stats["port"] | default(1936) | int) + 10000 }}
+    mode http
+    acl is_index path /
+    acl is_index path /index.html
+    http-request return status 200 content-type "text/html" file /etc/easyhaproxy/www/dashboard.html if is_index
+    http-request return status 404
 {% endif %}
 {% for o in data["easymapping"] -%}
     {% set mode = o["mode"] or "http" %}