feat(repo): add beta/pre-release packages

[ReenigneArcher]

Description

Add beta/pre-release package builds.

Screenshot

Issues Fixed or Closed

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Dependency update (updates to dependencies)
• Documentation update (changes to documentation)
• Repository update (changes to repository files, e.g. .github/...)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the in code docstring/documentation-blocks for new or existing methods/components

Branch Updates

LizardByte requires that branches be up-to-date before merging. This means that after any PR is merged, this branch
must be updated before it can be merged. You must also
Allow edits from maintainers.

• I want maintainers to keep my branch updated

[ReenigneArcher]

Some issues detected when adding this PR:

• latest beta sunshine cannot install dependencies using archlinux:base-devel image, even after updating archlinux-keyring, so moved back to archlinux/archlinux:base-devel, which unfortunately re-introduces Sunshine build cannot find suitable cuda compiler #2 (solved)
• pacman-repo-builder installs all packages, and I don't see a way to disable this... so beta packages will be in a separate pacman-repo... should they still be named sunshine-git, or just use the original name since they're in a different repo?