feat: implement openapi (#482)

apps/nextjs/src/app/api/openapi/route.ts

@@ -0,0 +1,8 @@
+import { NextResponse } from "next/server";
+
+import { openApiDocument } from "@homarr/api";
+import { extractBaseUrlFromHeaders } from "@homarr/common";
+
+export function GET(request: Request) {
+  return NextResponse.json(openApiDocument(extractBaseUrlFromHeaders(request.headers)));
+}