[core-http] support for nd-json payloads

[xirzec]

Monitor Exporter needs the ability to send NDJSON over the wire.

It's a pretty simple format, and I think this can be done easily in a policy after deserialization occurs by converting an outer JSON array into the newline-delimited format.

Example using Java code: https://github.com/srnagar/appinsights-demo/tree/master/com/azure/appins/demo