Consider improving Logstash configs in the docs/static/filebeat_modules/*/*.conf

These configs are part of the "adding Logstash to filebeat modules getting started experience" and therefore its very likely the first time a user will see a LS config.

For the best experience we should add a fair few comments to better inform what is going on. The user sees the nested field reference for the first time and there is a try three grok pattern scheme with two mutate renames that work only if earlier grok patterns fail that could be explained better.
Also, we should add grok and date parse failure handling.

Optionally, we could add anchors to Grok patterns.