Document single node failure recovery procedure (escluster)

[cbaxley]

Part of: #737 (Eng Spec: Add clustering support for Elasticsearch)

Description
As a system administrator, I want documentation on recovering from a single node failure so that I can restore full cluster capacity.

Acceptance criteria

• Documentation explains automatic shard redistribution (if replicas configured)
• Documentation covers replacing failed node hardware/VM
• Documentation covers running elasticsearch.yml on replacement node
• Documentation explains automatic shard rebalancing after node joins
• Documentation covers certificate and configuration requirements for new node
• Transpose the developer documents to the main documentation website.
• Quadlets don't get overwritten if they have custom code.