docs: add docs for experiements.deferImport (#12018)

Author: ahabhgk

website/docs/en/config/experiments.mdx

@@ -895,3 +895,12 @@ A side-effect-free module is a module that meets one of the following conditions
 :::
 
 > For more details, see [RFC: Lazy make for reexports in side effects free barrel file](https://github.com/web-infra-dev/rspack/discussions/11273)
+
+## experiments.deferImport
+
+<ApiMeta addedVersion="1.6.0" />
+
+- **Type:** `boolean`
+- **Default:** `false`
+
+When enabled, Rspack will support bundling the [Deferred Imports Evaluation](https://github.com/tc39/proposal-defer-import-eval) proposal, which allows deferring the evaluation of a module until its first use. Currently, only `import defer * as ns from "./module"` is supported, while `import.defer()` will be supported in future versions.

website/docs/zh/config/experiments.mdx

@@ -896,3 +896,12 @@ export default {
 :::
 
 > 更多详细内容可查看：[RFC: Lazy make for reexports in side effects free barrel file](https://github.com/web-infra-dev/rspack/discussions/11273)
+
+## experiments.deferImport
+
+<ApiMeta addedVersion="1.6.0" />
+
+- **类型：** `boolean`
+- **默认值：** `false`
+
+开启后 Rspack 会支持打包 [Deferred Imports Evaluation](https://github.com/tc39/proposal-defer-import-eval) 提案，该功能允许延迟模块的执行直到首次使用。目前仅支持 `import defer * as ns from "./module"`，`import.defer()` 会在后续版本支持。