Update Nixos config to use a hashedPasswordFile

[hansaskov]

For security reasons the hashed password should not be exposed to the internet as it could be seen as an attack vector. Instead we should store the hashed password in a separate file and reference it. Just like how the ssh keys are referenced.

• [x] Update config to use a separate file for the hashed password. docs
• [x] Purge git history for hashed password or change to new password
• [x] Improve server automation to require fewer steps (optional)

[hansaskov]

We will be using a new password