scope 10mb body limit to /monitors/import/json only

Address review feedback: keep the global express.json() at the default
100kb and mount a route-scoped 10mb parser in front of it for
/api/v1/monitors/import/json. Express matches middleware in registration
order, so the import route uses the larger parser and every other
endpoint keeps the tight default. No change in DoS surface for normal
traffic.

server/src/app.ts

@@ -54,7 +54,8 @@ export const createApp = ({
 
 	app.use(express.static(frontendPath));
 
-	app.use(express.json({ limit: "10mb" }));
+	app.use("/api/v1/monitors/import/json", express.json({ limit: "10mb" }));
+	app.use(express.json());
 	app.use(cookieParser());
 
 	app.use(sanitizeBody());