Use Elasticsearch 9.2's elasticsearch-rest5-client in spring-boot-elasticsearch

[filiphr]

Seems like that since the integration to use the new Elasticsearch Rest5Client was done in #46061 and from version 9.2.0 Elasticsearch is now also delivering a dedicated co.elastic.clients:elasticsearch-rest5-client.

With this PR I am adding that client to the managed dependencies and I have made the Java client co.elastic.clients:elasticsearch-java an optional dependency.

I believe that this is similar to how it was in Spring Boot 3 and similar to 4.0.0-M1.

[wilkinsona]

Thanks very much, @filiphr.

[anbusampath]

elasticsearch-rest5-client doesn't transitively pull elasticsearch-java. So spring-boot-elasticsearch module alone can't be used without adding elasticsearch-java. I also believe that this low level client created to keep clients compatible with Elasticsearch version 8 and below to support latest Apache client 5. elastic/elasticsearch-java#1064

[filiphr]

Hey @anbusampath, when I did this I didn't realize that there is now a spring-boot-starter-elasticsearch. The PR I did was for spring-boot-elasticsearch and to align that to how it was in Spring Boot 3. In Spring Boot 3 it was possible to only configure the low level Elasticsearch Rest Client, i.e. there was only spring-boot-starter-data-elasticsearch which brought the high level elastic-java dependency through spring-data-elasticsearch dependency.

In any case, in my opinion spring-boot-elasticsearch should not enforce the elasticsearch-java dependency on everyone. However, I do believe that it is OK for spring-boot-starter-elasticsearch to be a bit more opinionated and pull the elasticsearch-java dependency. I created #48141 for this. @wilkinsona, I'll leave it up to you and the Spring Boot team to decide whether the starter should be more opinionated or not.

[anbusampath]

However, I do believe that it is OK for spring-boot-starter-elasticsearch to be a bit more opinionated and pull the elasticsearch-java dependency.

This makes more sense.