Improvement: `setup-system update` should have less prompts

[balupton]

setup-system install should have the prompts, not setup-system update.

There is probably two steps for this:

1. having configuration options to specify defaults for all prompts
2. having shorter or no timeout for when defaults are provided: #77

[balupton]

@jondpenton you can rejoice now, updates will now generally only prompt for sudo, which you can manually reduce by config-edit --sudoers and increasing the timeout:
https://kagi.com/fastgpt?query=How+to+edit+%2Fetc%2Fsudoers+to+increase+the+timeout+value