Authentication Configuration

[vifino]

I read the nvme target source code again.
Turns out I was wrong about not needing host config.

Host configuration is required for authentication:

• /hosts/<nqn>/dhchap_key
• /hosts/<nqn>/dhchap_ctrl_key
• /hosts/<nqn>/dhchap_hash
• /hosts/<nqn>/dhchap_dhgroup

This might need a rethink, presumably requires tweaking the automatic allowed-hosts stuff as well.
I definitely do not want to have the config file contain hosts without encryption parameters.

Note: Needs CONFIG_NVME_TARGET_AUTH set, which isn't set by default and not explicitly on NixOS.