Integrate yay installation into archinstall process

[loxoron218]

describe the request

It would be a useful feature if archinstall could optionally install the AUR helper yay as part of the installation process. This would streamline the installation of AUR packages right after the base system setup, allowing users to immediately take advantage of AUR packages without requiring additional steps.

Maybe with something like this?

sudo pacman -Syyu --noconfirm git
git clone https://aur.archlinux.org/yay.git
(cd yay && makepkg -si --noconfirm)
sudo rm -rf ~/yay