Set JAVA_APP_DIR env var when necessary

When using Jib to build the container image
(and the defaults have not been changed),
JAVA_APP_DIR should be present in order to
avoid situations where agent jars cannot
be located.

Fixes: #39022
(cherry picked from commit 05fd6ff)

extensions/container-image/container-image-jib/deployment/src/main/java/io/quarkus/container/image/jib/deployment/JibProcessor.java

@@ -455,6 +455,7 @@ private JibContainerBuilder createContainerBuilderFromFastJar(String baseJvmImag
             // which would mean AppCDS would not be taken into account at all
             entrypoint = List.of(RUN_JAVA_PATH);
             envVars.put("JAVA_APP_JAR", workDirInContainer + "/" + JarResultBuildStep.QUARKUS_RUN_JAR);
+            envVars.put("JAVA_APP_DIR", workDirInContainer.toString());
             envVars.put("JAVA_OPTS_APPEND", String.join(" ", determineEffectiveJvmArguments(jibConfig, appCDSResult)));
         } else {
             List<String> effectiveJvmArguments = determineEffectiveJvmArguments(jibConfig, appCDSResult);