RHDEVDOCS-3177 Tracker for 1861266 - [DOCS] New USE_JAVA_VERSION variable not documented

Author: rolfedh

modules/images-other-jenkins-agent-env-var.adoc

@@ -50,4 +50,10 @@ JVM threads.
 |Specifies additional options for the Jenkins JVM. These options are appended to all other options, including the Java options above, and can be used to override any of them, if necessary. Separate each additional option with a space and if any option contains space characters, escape them with a backslash.
 |Example settings: `-Dfoo -Dbar`; `-Dfoo=first\ value -Dbar=second\ value`
 
+|`USE_JAVA_VERSION`
+|Specifies the version of Java version to use to run the agent in its container. The container base image has two versions of java installed: `java-11` and `java-1.8.0`. If you extend the container base image, you can specify any alternative version of java using its associated suffix.
+|The default value is `java-11`.
+
+Example setting: `java-1.8.0`
+
 |===