Remove usage of the Java High Level REST Client

[AlexElin]

The Java High Level REST Client is deprecated. See the https://opensearch.org/docs/latest/clients/java-rest-high-level/
Therefore there is sense to remove its usage in the next major version (2.0) of the spring-data-opensearch.

[krisfreedain]

@dlvenable can you look at this?

Catch All Triage - 1 2

[reta]

Yes, it is deprecated, I think we should deprecate the OpenSearchRestTemplate & Co first before removal