HSEARCH-5513 Add a "What's New" document for series

Author: marko-bekhta

documentation/src/main/asciidoc/public/whats-new/index.adoc

@@ -0,0 +1,81 @@
+// SPDX-License-Identifier: Apache-2.0
+// Copyright Red Hat Inc. and Hibernate Authors
+= What's New in {hibernateSearchVersion}
+:doctype: book
+:revdate: {docdate}
+:sectanchors:
+:anchor:
+:toc: left
+:toclevels: 4
+:docinfodir: {docinfodir}
+:docinfo: shared,private
+:html-meta-description: Hibernate Search, full text search for your entities - Reference Documentation
+:html-meta-keywords: hibernate, search, hibernate search, full text, lucene, elasticsearch, opensearch
+:html-meta-canonical-link: https://docs.jboss.org/hibernate/stable/search/reference/en-US/html_single/
+:title-logo-image: image:hibernate_logo_a.png[align=left,pdfwidth=33%]
+:html-meta-version-family: {hibernateSearchVersionShort}
+:version-selector-enabled: true
+:stem: latexmath
+
+== Dependency upgrades
+
+[[orm-version]]
+Hibernate ORM::
+Hibernate Search targets the Hibernate ORM 7.2 series.
+[[lucene-version]]
+Lucene::
+The Lucene backend now uses Lucene 9.12.2, while the `lucene-next` backend relies on Lucene 10.2.2
+[[elasticsearch-version]]
+Elasticsearch::
+The Elasticsearch backend works with Elasticsearch 9.2, as well as other already compatible versions.
+[[opensearch-version]]
+OpenSearch::
+The Elasticsearch backend works with OpenSearch 3.2 and 3.3, as well as other already compatible versions.
+
+[[pluggable-clients]]
+=== Pluggable Elasticsearch backend REST clients
+
+This version of Hibernate Search introduces pluggable REST clients for the Elasticsearch backend.
+Historically, the Elasticsearch backend relied on the Elasticsearch low-level REST client,
+which is based on Apache HTTP Client 4. With the new pluggable client architecture,
+it is possible to switch to a different REST client as needed.
+This may be useful when you are running Hibernate Search in an environment relying on a different HTTP client type (e.g. Vert.x).
+or when you need to use some distribution specific client features and need to switch to the OpenSearch REST client.
+
+Hibernate Search provides the following REST client options out of the box:
+
+[[backend-elasticsearch-configuration-client-elasticsearch-client-rest4]]
+==== Elasticsearch low level REST client (Apache HTTP Client 4)
+
+Coordinates::
+GroupID::: `org.hibernate.search`
+ArtifactID::: `hibernate-search-backend-elasticsearch-client-rest4`
+Underlying HTTP Client::: Apache HTTP Client 4
+
+This Elasticsearch backend REST client is based on the Elasticsearch low level client (`org.elasticsearch.client:elasticsearch-rest-client`).
+Currently, the default REST client used by the Elasticsearch backend.
+
+[[backend-elasticsearch-configuration-client-elasticsearch-client-rest5]]
+==== Elasticsearch low level REST client (Apache HTTP Client 5)
+
+Coordinates::
+GroupID::: `org.hibernate.search`
+ArtifactID::: `hibernate-search-backend-elasticsearch-client-rest5`
+Underlying HTTP Client::: Apache HTTP Client 5
+
+This Elasticsearch backend REST client is based on the newer Elasticsearch low level client (`co.elastic.clients:elasticsearch-rest5-client`),
+which is also used in the `co.elastic.clients:elasticsearch-java`.
+
+[[backend-elasticsearch-configuration-client-elasticsearch-client-opensearch]]
+==== OpenSearch low level REST client (Apache HTTP Client 5)
+
+Coordinates::
+GroupID::: `org.hibernate.search`
+ArtifactID::: `hibernate-search-backend-elasticsearch-client-opensearch-rest`
+Underlying HTTP Client::: Apache HTTP Client 5
+
+This Elasticsearch backend REST client is based on the OpenSearch low level client (`org.opensearch.client:opensearch-rest-client`).
+
+NOTE: It is recommended to explicitly add a client that you prefer as a dependency, since in the future version
+of Hibernate Search we will remove the implicit dependency on `hibernate-search-backend-elasticsearch-client-rest4`
+from the Elasticsearch backend.