[DOC] update the documentation to reflect the deprecated RestTransportClient

[Simon-Berhane-Paidy]

What do you want to do?
Hi there,

I learned from this page that the high level rest client is deprecated.
https://opensearch.org/docs/latest/clients/java-rest-high-level/

Then, I navigated to the java client documentation and was reviewing the options.
https://opensearch.org/docs/latest/clients/java/

One of the options says to use the Rest Client, without any deprecation notice. https://opensearch.org/docs/latest/clients/java/#installing-the-client-using-restclient-transport

So it made me think it's a different package that won't be deprecated. But looking at the source, I noticed this deprecation annotation.
https://github.com/opensearch-project/opensearch-java/blob/261cab4cf79e176b0892cfb44fad7c8cfaf44204/java-client/src/main/java/org/opensearch/client/transport/rest_client/RestClientTransport.java#L75

Am I correct then in assuming this will also be deprecated?
If so, I think mentioning this in the java client page would be very helpful.

Thanks!

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[hdhalter]

@VachaShah - Hi Vacha, can you please take a look at this and provide some guidance? Thanks!

[hdhalter]

Hi @wbeckler - Can someone on your team respond to this in Vacha's absence? Thanks!

[Xtansia]

In the current 2.x line of the Java client, the RestClientTransport is not yet deprecated. It will however be deprecated in a future 3.0.0 release, with eventual complete removal at a later date. As such it would be incorrect to declare it as deprecated in the documentation currently, but we could definitely make it clear the ApacheHttpClient5TransportBuilder is the preferred option and potentially telegraph RestClientTransport being slated for deprecation.

[hdhalter]

Thanks or the clarification, @Xtansia ! Can you please add the appropriate text to the file and create a PR? We'll then review it and get it published. Thanks.

[wbeckler]

I feel like that extended deprecation plan might be overly conservative. Where is it stated?

[Xtansia]

@wbeckler The main issue about the RestClientTransport deprecation specifically is this one: opensearch-project/opensearch-java#326