perf: change the default sort order of articles (#2480)

#### What type of PR is this?

/kind improvement
/milestone 2.0
/area core

#### What this PR does / why we need it:

修改文章列表的默认排序规则，之前是按照创建时间（createTime）升序，现在改为降序。即最新创建的文章在前面。

#### Special notes for your reviewer:

测试方式：

连续创建多篇文章，检查前后台的文章排序是否是最新的在最前面。

/cc @halo-dev/sig-halo 

#### Does this PR introduce a user-facing change?

```release-note
None
```

src/main/java/run/halo/app/content/PostSorter.java

@@ -73,7 +73,6 @@ public enum PostSorter {
         Function<Post, Instant> createTime =
             post -> post.getMetadata().getCreationTimestamp();
         return Comparator.comparing(createTime)
-            .thenComparing(name)
-            .reversed();
+            .thenComparing(name);
     }
 }