Rationalise Elasticsearch usecases and requirements for AA0.5

Elasticsearch is a generic document database solution that is highly scaleable, and will be used in multiple contexts throughout the telescope.  However, the complexity and design of Elasticsearch means that there is considerable overhead in deploying and managing the service, so it is desirable to - where possible - consolidate requirements and maintain a single Elasticsearch service.

This feature investigates the known dependencies for Elasticsearch in the SDP and Platform, and identifies the requirements, and develops a strategy for the design, deployment, management of a single implementation per telescope, that will also support the needs for independent deployment in other environments such as Dev, PSI, ITF.

In confluence:

• the operational requirements for the different Elasticsearch deployment contexts and usecases are identified and documented
• a strategy for managing (deployment, upgrade, configuration) of Elasticsearch is documented so that it can be implemented to coexist with the existing software delivery and deployment infrastructure