ES6 without TransportClient

https://docs.spring.io/spring-data/elasticsearch/docs/3.2.6.RELEASE/reference/html/#elasticsearch.clients says:

The well known TransportClient is deprecated as of Elasticsearch 7 and will be removed in Elasticsearch 8. (see the Elasticsearch documentation). Spring Data Elasticsearch will support the TransportClient as long as it is available in the used Elasticsearch version.

We strongly recommend to use the High Level REST Client instead of the TransportClient.

In this ticket we will migrate away from using TransportClient.

We are seeing strange serialization problems with the current client (like #515 (closed)) and the HighLevelRestClient defaults to Jackson Object mapping that may resolve some of the hidden problems (like UUID serialization hack in 84600c87)

Also please update to spring-data-elasticsearch@3.2.6.RELEASE.