Fix dynamic server usage in app router docs route

Currently in the app router docs route we read the request
headers directly from the original request object. This is
problematic because it leads to a dynamic server usage
error unless the docs endpoint is explicitly set to `force-dynamic`
caching strategy. By reading the headers from a cloned request
object the docs endpoint can be used with the default caching
strategy, fixing this issue.

packages/next-rest-framework/src/app-router/docs-route.ts

@@ -10,9 +10,12 @@ import {
 export const docsRoute = (_config?: NextRestFrameworkConfig) => {
   const config = getConfig(_config);
 
-  const handler = async (req: NextRequest, _context: { params: BaseQuery }) => {
+  const handler = async (
+    _req: NextRequest,
+    _context: { params: BaseQuery }
+  ) => {
     try {
-      const host = req.headers.get('host') ?? '';
+      const host = _req.clone().headers.get('host') ?? '';
       const html = getHtmlForDocs({ config, host });
 
       return new NextResponse(html, {