Documentation: Add remote_ip to example configuration

[jakelandis]

Fixes #249

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[jakelandis]

@acchen97 - Can you review the documentation change ?

I didn't see anywhere that we explicitly document the @metadata fields, so I just added it to the example.

How we document here should be similar to the TCP input which also has this value (as 5.0.0) logstash-plugins/logstash-input-tcp#81

[acchen97]

@jakelandis thanks for this. It might make sense to have a brief annotation for this. Thoughts around the below?

Incoming events from Beats include metadata information around the IP address of the host the Beat collected the event from. For example, this field can be accessed and enriched in the core event:

filter {
  mutate {
    add_field => { "remote_ip" => "%{[@metadata][ip_address]}" }
  }
}

[acchen97]

@jakelandis FYI, nice example from @suyograo on the Kafka plugin: logstash-plugins/logstash-input-kafka@cac9d59

[jsvd]

this looks like a quick win for improving users' experience and understanding, poking @jakelandis so this doesn't get stale

[Toffs-Rocky]

When I add this config, most events can get ip address, but some events show this value “%{[@metadata][ip_address]}”. Anyone encountered this problem?

[jakelandis]

closing this PR as stale