Adopt godot-ci for automated exports

[musjj]

https://github.com/abarichello/godot-ci provides a nice way to export and release your Godot games in a CI pipeline.

It would be cool if this project includes it in the template.

[jolexxa]

Hi! Thanks for the suggestion. We do need to support an export pipeline, but we'd probably do so with setup-godot as it runs directly on the GitHub runner. This makes it easier to produce build artifacts for every desktop platform since you can install whatever local toolchains you need the same as if you had a dedicated release computer.