feat(doc preview): add magic variable for file name

public/locales/en-US/dashboard.json

@@ -211,6 +211,7 @@
     "officePreviewServiceDes": "You can use following magic variables：",
     "officePreviewServiceSrcDes": "File URL",
     "officePreviewServiceSrcB64Des": " Base64 encoded file URL",
+    "officePreviewServiceName": "File name",
     "thumbnails": "Thumbnails",
     "localOnlyInfo": "The following settings only apply to local storage policies.",
     "thumbWidth": "Width",

public/locales/zh-CN/dashboard.json

@@ -211,6 +211,7 @@
     "officePreviewServiceDes": "可使用以下替换变量：",
     "officePreviewServiceSrcDes": "文件 URL",
     "officePreviewServiceSrcB64Des": " Base64 编码后的文件 URL",
+    "officePreviewServiceName": "文件名",
     "thumbnails": "缩略图",
     "localOnlyInfo": "以下设置只针对本机存储策略有效。",
     "thumbWidth": "缩略图宽度",

src/component/Admin/Setting/Image.js

@@ -255,6 +255,9 @@ export default function ImageSetting() {
                                     <br />
                                     <code>{"{$srcB64}"}</code> -{" "}
                                     {t("officePreviewServiceSrcB64Des")}
+                                    <br />
+                                    <code>{"{$name}"}</code> -{" "}
+                                    {t("officePreviewServiceName")}
                                 </FormHelperText>
                             </FormControl>
                         </div>