feat: Automatically switch to using "direct" ibmcloud s3 endpoints within VMs

[starpit]

If the rclone config points to an external ibmcloud s3 endpoint, we could automatically rewrite this to use the direct variant (cost-free) within the ibmcloud VMs.

I suppose the same holds in the other direction: if the rclone config points to a direct/private s3 endpoint, we in this case must rewrite this to use the public variant from the client.