Add ElasticSearch service

Created by: kostajh

We rely on it heavily for GrowthExperiments features and would be nice to have in PatchDemo; it would make the sites more realistic for QA / beta testing, etc.

I'm not sure how hard this would be to include in the current set up. I see a couple of options:

• use a service run on WCMS
• install ElasticSearch 6 via apt-get and friends; there is prior art for scripting this in vagrant but probably not easily adaptable for this project
• Run ElasticSearch via a Docker container. This seems to be the easiest, if we're OK with installing Docker. That would also simplify the process of adding other services, too.