Add S3 storage config example (#2005)

### What problem does this PR solve?
Add S3 storage config example

### Type of change
- [x] Documentation Update

conf/infinity_conf.toml

@@ -35,6 +35,14 @@ storage_type             = "local"
 # dump memory index entry when it reachs the capacity
 mem_index_capacity       = 1048576
 
+# S3 storage config example:
+# [storage.object_storage]
+# url                      = "127.0.0.1:9000"
+# bucket_name              = "infinity"
+# access_key               = "minioadmin"
+# secret_key               = "minioadmin"
+# enable_https             = false
+
 [buffer]
 buffer_manager_size      = "4GB"
 lru_num                  = 7