docs(iceberg): add documentation for batch_size server option (#522)

* docs(iceberg): add documentation for batch_size server option

* Update docs/catalog/iceberg.md

Co-authored-by: Copilot <[email protected]>

---------

Co-authored-by: Copilot <[email protected]>

Author: burmecia

docs/catalog/iceberg.md

@@ -160,6 +160,10 @@ For any server options need to be stored in Vault, you can add a prefix `vault_`
 
     For other optional S3 options, please refer to [PyIceberg S3 Configuration](https://py.iceberg.apache.org/configuration/#s3).
 
+#### Additional Server Options
+
+- `batch_size` - Controls the batch size of records read from Iceberg (default: 4096)
+
 ### Create a schema
 
 We recommend creating a schema to hold all the foreign tables: