Implement `passprompt`

[squell]

trafficstars

Describe the feature you'd like see implemented in sudo-rs The passprompt setting in /etc/sudoers

What problem can be solved with this feature? Allows settings the passprompt from the config file; this is a follow-up to #1252

Describe alternatives you've considered You can set the passprompt using -p and SUDO_PROMPT, but the benefit of passprompt is perhaps that it can be set on a per-command basis. I'm not entirely sure this is really a killer feature, though, and discussion on this enhancement is necessary since it does alter some flow in the critical pipeline (in the "apply policy to context" function).

Additional context There is also a passprompt_override setting (whose documentation in ogsudo doesn't seem to accurately describe its behaviour)