Add `Defaults: !admin_flag` to `/etc/sudoers`

Discord Message

Author: realami Channel: #feedback Link: https://discord.com/channels/1405685085923049482/1405686161791516873/1455282376795095176

Suggestion: add Defaults: !admin_flag to /etc/sudoers. Rationale: since exeuntu defaults to having a ~/.hushlogin file, there's no point in ~/.sudo_as_admin_successful being created when sudo is first run (this file is used to suppress the sudo hint in /etc/bash.bashrc, but .hushlogin already suppresses this hint). Having less detritus in ~ is better than having more. https://github.com/sudo-project/sudo/issues/56 has context.