Some 7.x ElasticSearch versions support some 6.x nodes, thus the version check
is inadequate. I am not sure there is a good way to check if a server
implements all the 7.x APIs, so check server version and minimum wire version
instead.
Nil unwrap causes the admin dashboard to crash/500 when the Chewy client info version number value is nil.
This occurs when running another ES-compatible backend such as MeiliSearch.
Obviously it would be good for chewy to recognise upstream but at least avoiding the crash would be fine.
