feat: post list supports displaying the pinned status (#720)

#### What type of PR is this?

/kind feature
/milestone 2.0.0-rc.2

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

支持在文章管理列表显示文章置顶标识。

#### Which issue(s) this PR fixes:

Fixes https://github.com/halo-dev/halo/issues/2678

#### Screenshots:

<img width="330" alt="image" src="https://user-images.githubusercontent.com/21301288/204138598-9a9265b2-cc2d-4fe6-9059-a804de72ca44.png">

#### Special notes for your reviewer:

测试方式：

1. 创建若干文章。
2. 将部分文章设置为置顶。
3. 返回到列表检查是否有置顶标识。

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


```release-note
Console 端支持在文章管理列表显示文章置顶标识。
```

src/modules/contents/posts/PostList.vue

@@ -801,6 +801,12 @@ const hasFilters = computed(() => {
                       <span class="text-xs text-gray-500">
                         评论 {{ post.stats.totalComment || 0 }}
                       </span>
+                      <span
+                        v-if="post.post.spec.pinned"
+                        class="text-xs text-gray-500"
+                      >
+                        已置顶
+                      </span>
                     </VSpace>
                   </template>
                 </VEntityField>