S3 doesn't work with literal IPv6 hosts

[juha-aiven]

When using S3Transfer with host being an IPv6 address such as ::1 Rohmu fails. This can happen when using a "non-S3 S3" such as MinIO and IPv6.

The exact reason of the failure is here:

rohmu/rohmu/object_storage/s3.py

Line 155 in a9aea97

custom_url = f"{scheme}://{host}:{port}"

According to RFC 2732

To use a literal IPv6 address in a URL, the literal address should be enclosed in "[" and "]" characters.

Obviously, the code doesn't do this.

I tried with a simple change and Rohmu seems to work.

            custom_url = f"{scheme}://[{host}]:{port}"