Implement user registration via SSH login

[TerrorBite]

When connecting via SSH, users should be able to create a new account and an initial character by selecting the appropriate option.

Requirements:

• When user is connecting via SSH, ask if they want to create an account.
• Collect user's password when registering an account.
• Collect user's SSH keys when registering so that those keys can later authenticate the user.
• Create new account in the backend for the registering user.
• Create initial character for the new user in the backend.
• Test that users can register new accounts.