add jackson 3 info (#1207)

Author: l-trotta

docs/getting-started.asciidoc

@@ -12,6 +12,7 @@ operations with it.
 * A JSON object mapping library to allow seamless integration of
 your application classes with the Elasticsearch API. The examples below
 show usage with Jackson.
+Jackson 3 is also supported, but to use it, Java 17 or later is needed.
 
 [discrete]
 === Installation 

docs/setup/installation.asciidoc

@@ -9,6 +9,7 @@ Requirements:
   support for https://github.com/FasterXML/jackson[Jackson] or a
   https://github.com/eclipse-ee4j/jsonb-api[JSON-B] library like
   https://github.com/eclipse-ee4j/yasson[Eclipse Yasson].
+  Jackson 3 is also supported, but to use it, Java 17 or later is needed.
 
 
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