Ingest varnish logs into ELK

The varnish access logs seems to be manually configured to be dumped on /var/log/varnish/varnishncsa.log (managed by the service varnishncsa) on moma

These logs are very useful to diagnose some issues and should be ingested in the elk cluster.

To do so, the varnishncsa service deployment, the logrotate configuration should be reintegrated in puppet and a filebeat configuration to ingest these logs declared.