Add alerting

• Add Blackbox exporter to easily export metrics about health of web services and DNS servers
• Add vmalert to throw alerts when something is wrong, with rich metadata (description, link to Grafana dashboard, criticity, etc)
• Add alertmanager to process throwed alerts and send them to Mattermost with nice formatting

pica-metrologie/alertmanager/Dockerfile

+ARG VERSION=v0.22.2
+
+FROM prom/alertmanager:${VERSION}
+
+COPY ./entrypoint.sh /entrypoint.sh
+COPY ./templates.tpl /config/templates.tpl
+
+# Initial image uses user nobody which cannot chmod nor sed
+USER root
+RUN chmod +x /entrypoint.sh
+
+ENTRYPOINT [ "/entrypoint.sh" ]
+CMD [ "--config.file=/etc/amtool/config.yml", "--storage.path=/alertmanager" ]