Use more sophisticated GitHub-Actions workflow instead of grunt-tasks

Currently, there is a huge grunt-configuration that builds, tests and releases Handlebars.

I would like to inspect this configuration and re-model it in GitHub actions and npm-scripts.

Does that make sense? I think it would help in building automated releases and we could migrate to more modern technologies independently of Grunt.

Start by inspecting the existing Grunt configuration and its build, test, and release tasks. Map those tasks to GitHub Actions workflows and npm scripts, then verify that builds, tests, and releases still run equivalently. The issue names no specific files or acceptance tests.

Written by the indexing model from the issue text.