[monitoring] Add permission to send pings to prometheus-blackbox-exporter

Signed-off-by: Yohann D'ANELLO <ynerant@crans.org>

roles/prometheus-blackbox-exporter/tasks/main.yml

 ---
+- name: Configure the exporter to allow pings
+  debconf:
+    name: "prometheus-blackbox-exporter"
+    question: "prometheus-blackbox-exporter/want_cap_net_raw"
+    value: "true"
+    vtype: "boolean"
+  notify: Restart prometheus-blackbox-exporter
+
 - name: Install Prometheus Blackbox exporter
   apt:
     update_cache: true