add haproxy scraping for use with builtin haproxy exporter

templates/conf/prometheus.yml.j2

@@ -96,3 +96,14 @@ scrape_configs:
         - {{ target }}:9117
 {% endfor %}
 {% endif %}
+
+{% if prometheus_haproxy_exporter_targets is defined %}
+  - job_name: haproxy
+    scrape_interval: 30s
+    scrape_timeout: 10s
+    static_configs:
+      - targets:
+{% for target in prometheus_haproxy_exporter_targets %}
+        - {{ target }}:8404
+{% endfor %}
+{% endif %}