Fix JavaDoc output directory (openhab#18064)

Signed-off-by: Holger Friedrich <[email protected]>

Author: holgerfriedrich

pom.xml

@@ -359,6 +359,7 @@ Import-Package: \\
           <artifactId>maven-javadoc-plugin</artifactId>
           <version>3.11.2</version>
           <configuration>
+            <outputDirectory>${project.build.directory}/site</outputDirectory>
             <failOnError>!${quality.skip}</failOnError>
             <tags>
               <tag>