refactor: autofill if post is published but no publish time (#4775)

#### What type of PR is this?
/kind improvement
/area core
/milestone 2.10.x

#### What this PR does / why we need it:
如果文章是发布状态但没有发布时间则自动填充

#### Does this PR introduce a user-facing change?
```release-note
None
```

application/src/main/java/run/halo/app/core/extension/reconciler/PostReconciler.java

@@ -113,6 +113,10 @@ public class PostReconciler implements Reconciler<Reconciler.Request> {
                     post.setStatus(status);
                 }
 
+                if (post.isPublished() && post.getSpec().getPublishTime() == null) {
+                    post.getSpec().setPublishTime(Instant.now());
+                }
+
                 // calculate the sha256sum
                 var configSha256sum = Hashing.sha256().hashString(post.getSpec().toString(), UTF_8)
                         .toString();

application/src/main/java/run/halo/app/core/extension/reconciler/SinglePageReconciler.java

@@ -112,6 +112,10 @@ public class SinglePageReconciler implements Reconciler<Reconciler.Request> {
 
     private void reconcileSpec(String name) {
         client.fetch(SinglePage.class, name).ifPresent(page -> {
+            if (page.isPublished() && page.getSpec().getPublishTime() == null) {
+                page.getSpec().setPublishTime(Instant.now());
+            }
+
             // un-publish if necessary
             if (page.isPublished() && Objects.equals(false, page.getSpec().getPublish())) {
                 unPublish(name);