"Actions v2"-enable gajira-cli

[imjohnbo]

Enables gajira-cli for Actions v2.

• [x] Add action.yml
• [x] Add build artifact, compiled using zeit/ncc (avoids having to npm install when running the action)
• [x] Add generic .gitignore from template
• [x] Additional package.json configuration
• [x] Update README.md
• [x] Remove Docker files
• [x] Add example workflow