chore(server): add auto index batch size (#12391)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **New Features**
  - Added a configurable batch size setting for automatic workspace indexing. Users can now adjust how many workspaces are indexed per batch, with a default value of 10 and support for values between 1 and 1000.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/backend/server/src/plugins/indexer/config.ts

@@ -19,6 +19,9 @@ declare global {
         username: string;
         password: string;
       };
+      autoIndex: {
+        batchSize: number;
+      };
     };
   }
 }
@@ -58,4 +61,9 @@ defineModuleConfig('indexer', {
     default: '',
     env: ['AFFINE_INDEXER_SEARCH_PASSWORD', 'string'],
   },
+  'autoIndex.batchSize': {
+    desc: 'Number of workspaces automatically indexed per batch',
+    default: 10,
+    shape: z.number().int().positive().max(1000),
+  },
 });