Spread load across all nodes in an elasticsearch cluster

What does this MR do?

Randomly shuffle the order of elasticsearch URLs when connecting to a multiple-node cluster

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

The Go repository indexer correctly spreads its load across all the nodes in the cluster. We want connections from Ruby (whether database or commits) to do the same.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #2911 (closed)