New subactions to implement

### Topic and scope of discussion
Now that we support multiple entry points, and thus "subactions", we can add multiple different actions. This should be a working draft of those subactions, and what they should do.

### Required

name | description
--- | ---
`setup` | The original main action, taking care of Expo/EAS CLI as well as authentication
`expo-build` | Create a new build using the classic build system
`expo-publish` | Create a new bundle to load in Expo Go
`eas-build` | Create a new build using EAS
`qr-code` | Create an Expo QR code and comment on a PR or commit, should support reference to build/publish actions or by `with`-inputs

### Optional

name | description
--- | ---
`expo-setup` | A simpler version of the main `setup`, but for Expo only
`eas-setup` | A simpler version of the main `setup`, but for EAS only

### Motivation
Makes using Expo in GH actions even easier.