feat: describe `addServerHandler`

docs/3.api/4.advanced/2.kit.md

@@ -2029,7 +2029,63 @@ export default defineNuxtModule({
 
 [source code](https://github.com/nuxt/nuxt/blob/main/packages/kit/src/nitro.ts)
 
-### `addServerHandler (handler)`
+### `addServerHandler`
+
+Adds a nitro server handler.
+
+#### Type
+
+```ts
+function addServerHandler (handler: NitroEventHandler): void
+
+export interface NitroEventHandler {
+  handler: string;
+  route?: string;
+  middleware?: boolean;
+  lazy?: boolean;
+  method?: string;
+}
+```
+
+#### Parameters
+
+##### `handler`
+
+**Type**: `NitroEventHandler`
+
+**Required**: `true`
+
+A handler object with the following properties:
+
+- `handler` (required)
+
+  **Type**: `string`
+
+  Path to event handler.
+
+- `route` (optional)
+
+  **Type**: `string`
+
+  Path prefix or route. If an empty string used, will be used as a middleware.
+
+- `middleware` (optional)
+
+  **Type**: `boolean`
+
+  Specifies this is a middleware handler. Middleware are called on every route and should normally return nothing to pass to the next handlers.
+
+- `lazy` (optional)
+
+  **Type**: `boolean`
+
+  Use lazy loading to import handler.
+
+- `method` (optional)
+
+  **Type**: `string`
+
+  Router method matcher.
 
 ### `addDevServerHandler (handler)`