Share Elasticsearch scripts and config
We currently have 3 separate places with the same or almost the same config and scripts,
- https://gitlab.com/gl-infra/gitter-infrastructure/tree/6ecdeb818563f44140dfb705c06f4ef3cd01fff1/ansible/roles/elasticsearch/instances/prod/files/elastic-config
- https://gitlab.com/gitlab-org/gitter/webapp/tree/157e8a0bee4ba121bb83c8848e443c93ae6271ff/scripts/docker/elasticsearch-image
- https://gitlab.com/gitlab-org/gitter/webapp/tree/157e8a0bee4ba121bb83c8848e443c93ae6271ff/scripts/docker/es
We should de-duplicate these so we don't have to update 3 places