[Filebeat][Doc] Elasticsearch output - loading index template missing index name option

[sherry-ger]

• Version: Filebeat 5.4.0

The option to set custom index name while configuring Elasticseach template is not included in the documentation - https://www.elastic.co/guide/en/beats/filebeat/current/filebeat-template.html#load-template-auto

As a part of configuring custom index template, it is common to add ones' own index name as well. The option is present and documented in the default filebeat.full.yml file.

  # Optional index name. The default is "filebeat" plus date
  # and generates [filebeat-]YYYY.MM.DD keys.
  #index: "filebeat-%{+yyyy.MM.dd}"

Please add this as a part of the filebeat get started guide as well.