Take advantage of space-time view for dataset center time

[whatnick]

datacube-ows version:
ows_config.py version/link::

Description

OWS depends on one type of metadata to in Datacube to infer centertime. Take advantage of the timerange stored in postgis materialized view to make this function better.

def dataset_center_time(dataset):

[SpacemanPaul]

dataset_center_time is used by GetFeatureInfo to report the precise date/time of the data.

We know from OWS config whether the product is a "summary" product or a "real-time" product, and we should be tuning our behaviour based on that.