tiered storage: add s3 endpoint for private s3 implementation

fix https://github.com/chrislusf/seaweedfs/issues/1238

weed/command/scaffold.go

@@ -380,6 +380,7 @@ sequencer_etcd_urls = "http://127.0.0.1:2379"
 	aws_secret_access_key = ""     # if empty, loads from the shared credentials file (~/.aws/credentials).
 	region = "us-east-2"
 	bucket = "your_bucket_name"    # an existing bucket
+	endpoint = ""
 
 # create this number of logical volumes if no more writable volumes
 # count_x means how many copies of data.