docs: explain how to use --rgw-dns-name to enable hostname style buckets

[tserong]

This is already handled by the charts for k8s deployments, but for dev/test or standalone usage, we should document somewhere to run with --rgw-dns-name YOUR_DOMAIN_NAME in case hostname style bucket access is desired. For example, in the ephemeral docker case you'd run something like this:

docker run -p 7480:7480 quay.io/s3gw/s3gw:latest --rgw-backend-store sfs --debug-rgw 1 --rgw-dns-name YOUR_DOMAIN_NAME

(This was originally reported on Slack at https://rancher-users.slack.com/archives/C04DCMUV8SE/p1696951336295009 when testing using a Java app using Amazon's S3Client class. This class apparently defaults to hostname style buckets, but can be made to using path style buckets by setting forcePathStyle = true.)

[jecluis]

For consistency with the project, I think this is the kind of thing that should also be wrapped by an entrypoint script. I kind of hate bleeing rgw options to the user.

[jecluis]

That and, when using the s3gw image, it should not be optional to use the sfs driver.

[tserong]

That and, when using the s3gw image, it should not be optional to use the sfs driver.

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