fix(kit): add typings to kit server middleware (#3776)

Co-authored-by: pooya parsa <pyapar@gmail.com>

packages/kit/build.config.ts

@@ -8,6 +8,7 @@ export default defineBuildConfig({
   externals: [
     '@nuxt/schema',
     'webpack',
-    'vite'
+    'vite',
+    'h3'
   ]
 })

packages/kit/src/server.ts

@@ -1,6 +1,12 @@
+import type { Middleware } from 'h3'
 import { useNuxt } from './context'
 
+export interface ServerMiddleware {
+  path?: string,
+  handler: Middleware | string
+}
+
 /** Adds a new server middleware to the end of the server middleware array. */
-export function addServerMiddleware (middleware) {
+export function addServerMiddleware (middleware: ServerMiddleware) {
   useNuxt().options.serverMiddleware.push(middleware)
 }