Add object storage config to doc (#2049)

### What problem does this PR solve?
Add object storage config to doc

### Type of change

- [x] Documentation Update

docs/references/configurations.mdx

@@ -122,6 +122,21 @@ compact_interval         = "120s"
 # The system performs a flush operation for that in-memory index
 # Range : [8192, 8388608]
 mem_index_capacity       = 1048576
+# Storage type. Including local, minio. Default to local  
+storage_type             = "local"
+
+# Object storage configuration
+[storage.object_storage]
+# URL of the object storage server
+url                      = "127.0.0.1:9000"
+# The bucket where store the data
+bucket_name              = "infinity"
+# Access key of object storage server
+access_key               = "minioadmin"
+# Secret key of object storage server
+secret_key               = "minioadmin"
+# Using http or https protocol
+enable_https             = false
 
 # Buffer manager configuration
 [buffer]