add: eruption-git

[Rachel7is7out7jet]

This pull request adds a new Pacscript for Pacstall to install Eruption, an open-source software used to control RGB lighting and effects on supported Roccat hardware.

The Pacscript enables and starts the eruption.service systemd service, as it is essential for Eruption to function correctly.
Optional user-level systemd services provided by Eruption (used for additional effects) are not enabled automatically, allowing users to opt in only if they need them.

The Pacscript is based on:

• The official Eruption source code and documentation from the upstream repository (https://github.com/eruption-project/eruption)
• The existing eruption-git PKGBUILD from the Arch User Repository (AUR), which served as a reference for build steps, dependencies, and runtime requirements (https://aur.archlinux.org/cgit/aur.git/tree/PKGBUILD?h=eruption-git)

[Elsie19]

The arch variable must be included!