Add support for --etcd-s3 options to backup etcd snapshots to s3 #55
Description
In order to get automated backup of scheduled or on-demand etcd snapshots, I need to leverage k3s support for writing and restoring snapshots from S3
See https://docs.k3s.io/cli/etcd-snapshot
K3s supports writing etcd snapshots to and restoring etcd snapshots from systems with S3-compatible APIs. S3 support is available for both on-demand and scheduled snapshots.