[release-2.0] feat: archives in descending order by month (#2975)

This is an automated cherry-pick of #2959

/assign JohnNiang

```release-note
归档数据按月降序
```

src/main/java/run/halo/app/theme/finders/impl/PostFinderImpl.java

@@ -259,12 +259,13 @@ public Mono<ListResult<PostArchiveVo>> archives(Integer page, Integer size, Stri
                         // convert to archive year month value objects
                         List<PostArchiveYearMonthVo> monthArchives = monthPosts.entrySet()
                             .stream()
-                            .sorted(Map.Entry.comparingByKey())
                             .map(monthEntry -> PostArchiveYearMonthVo.builder()
                                 .posts(monthEntry.getValue())
                                 .month(monthEntry.getKey())
                                 .build()
                             )
+                            .sorted(
+                                Comparator.comparing(PostArchiveYearMonthVo::getMonth).reversed())
                             .toList();
                         return PostArchiveVo.builder()
                             .year(String.valueOf(key))