Add response fields to Kibana module based on ECS

[ruflin]

This is based on the ECS http fields: https://github.com/elastic/ecs#http

[ruflin]

I'm not happy with the naming of this field as it's more the duration of the request and does not directly belong to the response?

[ruflin]

This is probably what we have in heartbeat under http.rtt.total: https://github.com/elastic/beats/blob/master/heartbeat/monitors/active/http/_meta/fields.yml#L85

[ruflin]

Any suggestions?

[andrewkroh]

I think the term "response time" is pretty ubiquitous so wouldn't change it. IIUC this field contains the elapsed time between request received to responses sent by the Kibana server. So if anything you could work in "elapsed" to the name to emphasize that this is a duration rather that a date (e.g. http.response.elapsed_time).

[ruflin]

I like the suggestion, changed to elapsed_time