docs: config to rootConfig

Signed-off-by: Vincenzo Scamporlino <vincenzos@spotify.com>

docs/backend-system/building-backends/01-index.md

@@ -61,11 +61,11 @@ All of these services can be replaced with your own implementations if you need
 For example, let's say we want to customize the core configuration service to enable remote configuration loading. That would look something like this:
 
 ```ts
-import { configServiceFactory } from '@backstage/backend-app-api';
+import { rootConfigServiceFactory } from '@backstage/backend-app-api';
 
 const backend = createBackend({
   services: [
-    configServiceFactory({
+    rootConfigServiceFactory({
       remote: { reloadIntervalSeconds: 60 },
     }),
   ],

docs/backend-system/core-services/01-index.md

@@ -183,11 +183,11 @@ There's additional configuration that you can optionally pass to setup the `conf
 You can configure these additional options by adding an override for the core service when calling `createBackend` like follows:
 
 ```ts
-import { configServiceFactory } from '@backstage/backend-app-api';
+import { rootConfigServiceFactory } from '@backstage/backend-app-api';
 
 const backend = createBackend({
   services: [
-    configServiceFactory({
+    rootConfigServiceFactory({
       argv: [
         '--config',
         '/backstage/app-config.development.yaml',