Ship more logs to logstash/elasticsearch

Some of our infrastructure (I'm looking at you Apache) directly logs to files, and is awkward to make log to syslog/journald.

It'd be nice to have those logs shipped to elasticsearch, so we can minimize local disk usage on our infrastructure, and minimize the time we spend looking for logs when something goes wrong.

The canonical log shipper for the Logstash stack seems to be https://www.elastic.co/products/beats; most notably "filebeat". elastic provides an apt repository with their "beats", documentation at https://www.elastic.co/guide/en/beats/libbeat/current/setup-repositories.html.

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Migrated from T791 (view on Phabricator)