Setup CI

[ErisApps]

Reworks the GH actions workflow based on the prototyping and development that has been done over the course of the (roughly) past 6 months.

• Adjusted repository structure that separates the source code more clearly from non-source code files.
• Leverages the beta 7 of BSMT.T which fixes a few more bugs that had been uncovered during prototyping the new workflow.
• Leverages nuke-build/nuke and the newly developed helper package ErisApps/BeatSaberModdingTools.Nuke, the latter being based upon:
  • Goobwabber/download-beatmods-deps
  • ProjectSIRA/download-sira-stripped
• The version is now automagically calculated by GitVersion, by looking up all tags, when building through Nuke.

Based on the prototype that can be found here: ErisApps/NukeBuildTesting