Move elasticsearch over to using the same cluster as PlanningAlerts

[mlandauer]

This will mean less to maintain and the Elasticsearch cluster that we're using for PlanningAlerts has redundancy and is donated to us by elastic.co.

We're currently using version 2.4.6 in production locally

The cluster is using 6.8.23

We're currently using searchkick 1.5.1. We will probably need to upgrade the gem to support elasticsearch 6.8.23.

[mlandauer]

The latest version of searchkick supports elasticsearch 6. See https://github.com/ankane/searchkick

[mlandauer]

So, a rough plan for a not horrible migration with downtime is:

• Use a local copy of the production database (a reasonably recent copy).
• Point the local development version at the new cluster and reindex everything.
• Test that it all works.
• Use a new setting for the new server. Set that up in production.
• Deploy a new version of the app with an updated searchkick using the new setting. This can be deployed and rolled back if need
• Do a full reindex in production
• Rename the setting and tidy up

[mlandauer]

That's done now. The main code changes that made this possible:

• https://github.com/openaustralia/publicwhip/commit/39ad57d125730b932a192b3ee561437ea3791295
• https://github.com/openaustralia/publicwhip/commit/0d15c30aa293646c771c3ee21263097e4c981256
• https://github.com/openaustralia/infrastructure/commit/923a3191bd402dd8caf751ffda1450961123a827