[ECS] Addition - http.request.header.bytes & http.response.header.bytes

[ScottElastic]

Please fill in the following sections describing your proposed changes: -->
Ref: https://www.elastic.co/guide/en/ecs/current/ecs-http.html

Today, ECS has 2 fields for http request size:

http.request.body.bytes - body size in bytes
http.request.bytes - header+body size in bytes

It would be beneficial to have a field dedicated to the size of the headers as well, for ex:

http.request.header.bytes - header size in bytes

similarly for
http.response.header.bytes

To have more accurate detailed information on the http request without requiring math to be done by the end user.

[jamiehynds]

@ScottElastic have you come across any sample logs whereby the bytes values are exposed and thus could easily be mapped to these proposed fields? or would there be some calculations required in order to populate the fields?

@ebeahan any thoughts on these proposed fields?

[trisch-me]

@ScottElastic do you have concrete examples where we would use this data or how to get this data?
I also suggest to put this kind of question into Otel repo as we are donating ECS to the Otel so would be great to have everything in 1 place.
If you have already use cases I can help to make a PR into otel community