[Observium] Add Device API - Option to provide poller id as parameter.

Hi All,

I am using observium apis to add devices to observium in a partitioned poller setup.

But the current add device api (POST /api/v0/devices/) is not accepting poller_id as a parameter. Currently I am using MySQL Query to add devices to observium with poller_id.

I could see that the API is in active development state. So it will be great if you can incorporate this request as well.

Best, Midhun Kandoth