feat: adapt the target attribute of the menuitem (#56)

适配 MenuItem 的 target 属性，支持设置菜单打开方式，参考：

- https://docs.halo.run/developer-guide/theme/finder-apis/menu
- halo-dev/halo#3072

注意，因为 target 属性是在 2.1.0 之后添加的，所以主题的 requires 设置为了 `>=2.1.0`。

/kind feature

```release-note
适配 Halo 菜单项打开方式的设置。
```

templates/modules/header.html

@@ -29,6 +29,7 @@
             class="text-gray-600 hover:text-blue-600 dark:text-slate-50 dark:hover:text-gray-300"
             th:href="@{${menuItem.status.href}}"
             th:text="${menuItem.status.displayName}"
+            th:target="${menuItem.spec.target?.value}"
           ></a>
           <ul
             th:if="${not #lists.isEmpty(menuItem.children)}"
@@ -51,6 +52,7 @@
                 class="h-full w-full truncate px-4 py-2 text-gray-600 hover:text-blue-600 dark:text-slate-50 dark:hover:text-gray-300"
                 th:href="@{${childMenuItem.status.href}}"
                 th:text="${childMenuItem.status.displayName}"
+                th:target="${childMenuItem.spec.target?.value}"
               ></a>
             </li>
           </ul>
@@ -189,7 +191,7 @@ <h2 class="text-sm font-medium text-gray-600 dark:text-slate-300">菜单</h2>
       <nav class="mt-6">
         <ul class="-my-2 divide-y divide-gray-100 text-sm text-gray-800 dark:divide-slate-800 dark:text-slate-100">
           <li th:each="menuItem : ${menu.menuItems}">
-            <a class="flex items-center justify-between gap-1 py-2" th:href="@{${menuItem.status.href}}">
+            <a class="flex items-center justify-between gap-1 py-2" th:href="@{${menuItem.status.href}}" th:target="${menuItem.spec.target?.value}">
               <span th:text="${menuItem.status.displayName}"></span>
             </a>
             <ul class="divide-y divide-gray-100 dark:divide-slate-800" th:if="${not #lists.isEmpty(menuItem.children)}">
@@ -198,6 +200,7 @@ <h2 class="text-sm font-medium text-gray-600 dark:text-slate-300">菜单</h2>
                   class="h-full w-full truncate px-4 py-2 text-gray-600 dark:text-slate-200"
                   th:href="@{${childMenuItem.status.href}}"
                   th:text="${childMenuItem.status.displayName}"
+                  th:target="${childMenuItem.spec.target?.value}"
                 ></a>
               </li>
             </ul>

theme.yaml

@@ -14,4 +14,4 @@ spec:
   settingName: "theme-earth-setting"
   configMapName: "theme-earth-configMap"
   version: 1.2.0
-  require: 2.0.0
+  require: ">=2.1.0"