Proxy mapping request to ES from /flow/{name}/mapping

[wrathagom]

Goal being that all communication should go through the Ingest API for channel creation. Part of channel creation could be defining a mapping for the index.

[milutz]

@malave Is this done? in progress? on hold?

[malave]

@milutz I haven't started with this yet.

[wrathagom]

@milutz should we take the opportunity when we implement this to simplify the the mapping definition at all? or is it literally just a passthrough.