Add endpoint_url so we can copy from external s3 services

[Xuanwo]

We should disallow endpoint like http://127.0.0.1 by default.

[Xuanwo]

/assign

[ZeaLoVe]

In the stateful test, minio is as databend storage, but the dataset is in s3. #6171 need this feature.

[Xuanwo]

I will address this ASAP.