feat: add support for hetnzer cloud s3 storage

[the-technat]

This adds support for Hetzner Cloud as provider for object storage.

Hcloud S3 is currently in beta and not yet officially announced. However there are already official docs about it and it's listed as an entry in the Hcloud console. I received beta access this week and used their S3 together with this action here. Since I had to workaround the missing provider I thought I'll try and contribute it here.

As region, Hetzner currently only provides fsn1.

Let me know what you think.