[JENKINS-64356] fix legacyIds missing when creating jobs via REST API or CLI (#9303)

* [JENKINS-64356] call onCreatedFromScratch after creating item via api or cli

When creating jobs via the rest api or cli the call to
onCreatedFromScratch was missing. This can lead to long startup times
when many jobs are created this way.

* remove unused import

core/src/main/java/hudson/model/ItemGroupMixIn.java

@@ -290,6 +290,7 @@ public abstract class ItemGroupMixIn {
 
             add(result);
 
+            result.onCreatedFromScratch();
             ItemListener.fireOnCreated(result);
             Jenkins.get().rebuildDependencyGraphAsync();