Allow restricting snapshot management commands to acting on preconfigured paths and backends

Is your feature request related to a problem? Please describe. Currently, cluster administrators can use the k3s etcd-snapshot CLI (or undocumented snapshot HTTP API) to create and delete snapshots against any local filesystem path or S3-compatible backend. The paths and/or backends do not necessarily have to be the same as those configured for scheduled snapshots, which allows administrators a high level of flexibility.

Describe the solution you'd like Some administrators have asked for the ability to restrict on-demand snapshots and snapshot management commands (delete) to using the same snapshot directory and/or etcd backend configuration as scheduled snapshots. This offers administrators a sense of security in the form of knowing that etcd snapshots can only be created or deleted against predefined paths and backends, at the cost of reduced flexibility.

Describe alternatives you've considered Not have this feature, and continue to allow administrators to create/delete snapshots against any path or storage backend.

Additional context