Permission denied when saving key

[sandlbn]

The container was failing to save the key with the following error:

thread 'main' panicked at src/main.rs:608:61:
Failed to save key: Os { code: 13, kind: PermissionDenied, message: "Permission denied" }
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

This happened because the /data directory was created after switching to the non-root appuser, resulting in incorrect ownership and write permissions.

[marcelamelara]

LGTM