Add `doas` support.

[iguanajuice]

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This will make all 11 doas users very happy :)

[thias]

Why not :sweat_smile: But could you please update the logic (since not having sudo doesn't guarantee doas will be there) as well as make it more consistent with the other checks? Something like:

# Alias sudo to doas if found
if which doas &>/dev/null; then

Or change to check for both sudo's absence and doas existence if sudo should be preferred if available.

[iguanajuice]

Fixed up the syntax. Also, if neither doas nor sudo is found, use good ol' su -c