`elastic_search` Handler Does Not Work (Invalid Factory Parameters)

[Kenneth-Sills]

As noted here, using type: elastic_search for a handler does not work. We attempt to pass the host as host, but the ClientBuilder::fromConfig from upstream expects a plural hosts array.

This applies to both v7 and v8. There are no workarounds, except to install the Elastica client instead (v7 due to #499).

We have no tests for elastic_search handlers.