Store session info for long time non interactive auth

[rekby]

Hello.

Thanks for the CLI it is great way for update certificate on synology.

1. I don't want to store login/password as plain text
2. I have enabled 2-factor auth for administrators.

Now CLI doesn't support the cases for use in authomation

What you think about

1. Add optional otp-code (will use for auth request)
2. Option for save auth data (session, token) into a file and use the file for next commands

I can create PR with the functions if you are ok.

[reddec]

@rekby, thanks for the idea! As soon as this features will be backward compatible (ie existent users will not need to change their config - for example, it can be done by optional flag/env) I will greatly appreciate PR.

[glarizza]

+1 on this, it would be great to have the ability to use syno-cli with accounts that have 2-factor auth enabled!