Investigate using TimescaleDB in Datastore

We have a very lightweight wrapper around PostgreSQL for the CKAN datastore. Now that we're extending the datastore for [faster performance, etc](https://ckan.org/2017/08/10/faster-datastore-in-ckan-2-7/), it might pay to look into integrating TimescaleDB as well.

This further enables CKAN to handle use cases beyond data publishing (e.g. streaming data, smart city, data exchange, etc.). And if its packaged as a PostgreSQL extension, it should be largely transparent to CKAN.

cc @wardi @davidread @akulkarni @mfreed

Start by reviewing CKAN’s lightweight PostgreSQL wrapper for the datastore and the linked datastore performance context. Investigate whether TimescaleDB can be integrated as a PostgreSQL extension for streaming and related use cases, and document a clear feasibility recommendation or integration proposal.

Written by the indexing model from the issue text.