Breakup .gitlab-ci.yml into unity specifics to ease integration.
The goal here is to:
- Make it clear which parts of the .gitlab-ci are unity specific
- Try to carve off items that are specific to the ci of unity to another file to ease updating should things change
- Add comments to indicate how people can modify the .gitlab-ci effectively.
I added this because in adopting this .gitlab-ci for my project I wasn't clear how I could extend things, what was free to modify, etc.