chore: annotated ConfigurationChangedListener to prevent compil error…

… in IDEA

Signed-off-by: Andre Dietisheim <adietish@redhat.com>

src/main/java/com/redhat/devtools/intellij/telemetry/core/configuration/TelemetryConfiguration.java

@@ -153,6 +153,7 @@ public static Mode valueOf(boolean enabled) {
         }
     }
 
+    @FunctionalInterface
     public interface ConfigurationChangedListener {
         Topic<ConfigurationChangedListener> CONFIGURATION_CHANGED =
                 Topic.create("Telemetry Configuration Changed", ConfigurationChangedListener.class);