feat: use custom @ import dialog (#8723)

[BS-1747](https://linear.app/affine-design/issue/BS-1747/[ui]-通过导入的ui还是旧的，需要更新)

packages/common/infra/src/modules/feature-flag/constant.ts

@@ -167,6 +167,7 @@ export const AFFINE_FLAGS = {
     displayName: 'Enable Snapshot Import Export',
     description:
       'Once enabled, users can import and export blocksuite snapshots',
+    hide: true,
     configurable: true,
     defaultState: false,
   },