Automated releases using GH Actions

[redtide]

Currently Carla-Releases are made manually in a local configuration via build.sh using PawPaw' build scripts, then uploaded on GitHub after a tag.
The idea would be:

• Remove Carla-Releases, moving/adapting the build.sh script in Carla repository.
• In Carla build workflow, add a deploy job, to push specified artifacts to GitHub Releases on its repository.
• PawPaw should not be a git submodule, but downloaded like any external dependency during the CI workflow.

That is, when tagging a new release, GitHub Actions will run the additional deploy job, unused in normal commits, its purpose is to push the built artifacts on the GitHub Releases section.
It will use the usual build jobs with specified additional steps not running on normal commits, e.g. a different/additional script or making a Windows installer instead of a simple zip.
Once successful, the releases will be uploaded without manual intervention.