Add pacman hook support

Pacman support hooks to run after updating packages (see https://wiki.archlinux.org/title/Pacman#Hooks). These reside either in /usr/share/libalpm/hooks or /etc/pacman.d/hooks.

After an "pacman -Suy" completed I commonly run "systemctl restart patchmon-agent.service" to push the information to the patchmon server. This could be automated by the following patchmon-agent.hook

[Trigger]
Operation = Install
Operation = Upgrade
Operation = Remove
Type = Package
Target = *

[Action]
Description = Pushing update information to patchmon
Exec = /usr/bin/systemctl restart patchmon-agent.service
When = PostTransaction
NeedsTargets