[Heartbeat] Non-UTF8 HTTP Response Bodies Silently Disappear

[andrewvc]

We can't do much with non-UTF8 response bodies in terms of outputting them to the console or ES since the go JSON encoder will replace them with empty strings (and ES won't index them anyway).

However we should document this behavior and possible add a new field http.response.body.encoding field that shows the encoding of the body.

[elasticmachine]

Pinging @elastic/uptime (:uptime)

[botelastic]

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