[JENKINS-72958] expose PrimaryInstanceMetadataAction to API (#259)

Author: MarkRx

src/main/java/jenkins/scm/api/metadata/PrimaryInstanceMetadataAction.java

@@ -33,6 +33,7 @@
 import jenkins.scm.api.SCMNavigator;
 import jenkins.scm.api.SCMSource;
 import jenkins.scm.api.SCMSourceEvent;
+import org.kohsuke.stapler.export.ExportedBean;
 
 /**
  * Identifies a {@link SCMHead} / {@link SCMSource} as being a primary instance. Some examples of how this metadata is
@@ -70,6 +71,7 @@
  *
  * @since 2.0.1
  */
+@ExportedBean
 public class PrimaryInstanceMetadataAction extends InvisibleAction implements Serializable {
     /**
      * Ensure consistent serialization.