Changes system property name from enabled to defaultValue

Thanks @jtnord.

Co-Authored-By: James Nord <jtnord@users.noreply.github.com>

Author: alecharp

core/src/main/java/jenkins/model/experimentalflags/BooleanUserExperimentalFlag.java

@@ -25,6 +25,7 @@
 package jenkins.model.experimentalflags;
 
 import edu.umd.cs.findbugs.annotations.NonNull;
+import jenkins.util.SystemProperties;
 
 /**
  * @since 2.395
@@ -36,7 +37,7 @@ protected BooleanUserExperimentalFlag(@NonNull String flagKey) {
 
     @Override
     public @NonNull Boolean getDefaultValue() {
-        return Boolean.getBoolean(getClass().getName() + ".enabled");
+        return SystemProperties.getBoolean(getClass().getName() + ".defaultValue");
     }
 
     @Override