This patch adjust the key to use the armored format, which flux supports

This reverts commit 342a9382.

Since the secrets path is only available inside the container, but the
systemd-run command is executed outside the container, it can't access
the secret path, therefore the file needs to be copied.

This patch fixes issues currently faced by longhorn, where the SELinux
policy denies a DAC_override for iscsid. Since I couldn't find on what
file it even tries to do this override, for now, this override to fix
unmountable volumes.

This patch should provide an automated backup for all postgresql
clusters in the cluster. This implementation is less than ideal, due to
technical sharing of backups among all namespaces, but for now, it's
better than no backup. There will be further work on separating these
backups, but it is what it is for now.