Elasticsearch migrations should not start until after a deployment is finished

Problem

At present the Elasticsearch migrations will just kick off every 30 minutes and depending on the sidekiq worker that picks up the job it may happen that we start a migration during a deployment. This may have weird consequences depending on whether some parts of the application are running older code, especially if the migration finishes before the deployment.

Solution

We already have some mechanism in our deployments which triggers post deployment database migrations after all servers have had the code updated. We should probably do the same thing for Elasticsearch migrations.