Add support for Elasticsearch 7.x (#12053)

- Check ES server version by querying its API

- Minimum required version of ES is 5.x

- Add deprecation warnings for ES versions < 7.x

- Still works with 5.x and 6.x, but support to be removed at a later date.

Signed-off-by: Aditya Manthramurthy <aditya@minio.io>

go.mod

@@ -24,6 +24,7 @@ require (
 	github.com/dswarbrick/smart v0.0.0-20190505152634-909a45200d6d
 	github.com/dustin/go-humanize v1.0.0
 	github.com/eclipse/paho.mqtt.golang v1.3.0
+	github.com/elastic/go-elasticsearch/v7 v7.12.0
 	github.com/fatih/color v1.10.0
 	github.com/fatih/structs v1.1.0
 	github.com/go-ldap/ldap/v3 v3.2.4