CEPH compatibility

[mastnym]

Hi there, at first - thanks for the plugin. This is not a bug, just info, maybe recommendation for others. We use this plugin to connect moodle to our ceph storage(https://docs.ceph.com/en/latest/radosgw/). Ceph use S3 backend, but there are some modifications you need to make to make this work

• CEPH does not use (as far as I know) subdomain style buckets, but path style buckets, so another config options which is not available in UI is needed to be set
• CEPH does not require S3 region to be set. In fact, region has to be empty to make everything work

Feel free to look at these small modifications at my github

If developers would be interested in making CEPH a compatible storage I'd:

• either add use_path_style_endpoint setting to plugin settings (defaults to false) or introduce ceph as a filesystem somehow which sets this option automatically
• let region option to be blank for ceph (should not be allowed to stay empty anyway for S3 which needs it populated as far as I know)

Thats it