Integrate HugeCTR into the new Triton ensemble API

[karlhigley]

Provide support for serving HugeCTR models in Merlin Systems

[viswa-nvidia]

@karlhigley , which roadmap ticket does this map to ?

[karlhigley]

@viswa-nvidia This never mapped to a roadmap ticket, it was started (and mostly completed) on our own initiative during the stretch of time when the roadmap tickets didn't cover Systems.

[viswa-nvidia]

@oliverholworthy , please link the relevant ticket/PR. Tag the relevant cuDF team in this ticket