fix: introducing "flatten" profile to use the plugin (#984)

The plugin is not needed in this project but it's used in the
downstream Java repositories.

By specifying the profile in "Build with Airlock" check, we can
ensure the required dependencies are available in Airlock.

Author: suztomo

java-shared-config/pom.xml

@@ -728,5 +728,18 @@
         </plugins>
       </build>
     </profile>
+    <profile>
+      <!-- Profile to use the flatten plugin. This is useful for testing
+        the availability of the dependencies in Airlock. -->
+      <id>flatten</id>
+      <build>
+        <plugins>
+          <plugin>
+            <groupId>org.codehaus.mojo</groupId>
+            <artifactId>flatten-maven-plugin</artifactId>
+          </plugin>
+        </plugins>
+      </build>
+    </profile>
   </profiles>
 </project>