Refactor image upload method to client-side download (#14)

重构图片上传的方案，改为先在客户端下载，然后调用上传文件的接口上传到附件。

此改动主要考虑到服务器网络环境问题，可能在服务器无法访问 Unsplash 服务或者速度缓慢。

/kind improvement

```release-note
重构图片上传的方案，改为先在客户端下载，然后调用上传文件的接口上传到附件。
```

console/src/components/UnsplashSelectorProvider.vue

@@ -317,15 +317,19 @@ async function downloadSinglePhoto(photo: Photo) {
   try {
     const { policyName, groupName, urlType } = basicConfig.value?.downloadMode || {}
 
-    const { data: newAttachment } = await axiosInstance.post<Attachment>(
-      `/apis/api.console.halo.run/v1alpha1/attachments/-/upload-from-url`,
-      {
-        url: photo.urls[urlType || 'raw'],
-        filename: `${photo.alt_description?.toLowerCase().replace(/\s+/g, '-') || photo.id}.jpg`,
-        policyName: policyName,
-        groupName: groupName
-      }
-    )
+    const imageResponse = await fetch(photo.urls[urlType || 'raw'])
+
+    const imageBlob = await imageResponse.blob()
+
+    const { data: newAttachment } = await consoleApiClient.storage.attachment.uploadAttachment({
+      file: new File(
+        [imageBlob],
+        `${photo.alt_description?.toLowerCase().replace(/\s+/g, '-') || photo.id}.jpg`,
+        { type: imageBlob.type }
+      ),
+      policyName: policyName as string,
+      groupName: groupName
+    })
 
     await bindingAttachmentMutate({
       attachment: newAttachment,