replace sudo with run0

• With new systemd 256 run0 is added as replacement for sudo.
• This MR replaces sudo with run0
• the pkexec check is needed to ensure that polkit is installed, else run0 always fails.

For the same reason that doas can't be replaced this way, run0 can't either.

!260 (comment 187153)

run0 seems to have --setenv=NAME[=VALUE], so it does not seem impossible That of course does not mean that its necessarily a desirable change

mentioned in issue pacman/pacman-contrib#131

mentioned in issue archlinux/packaging/packages/base-devel#5 (closed)