fix: react build dist declaration file

[chedieck]

Related to #505

Description

Fixes #505.

Test plan

1. Move paybutton-config.json to react/lib/paybutton-config.json.
2. Then, inside react/, run yarn build.
3. Make sure the react/dist/ directory tree is being built like:

dist/
├── index.d.ts
├── index.js
├── index.js.map
├── index.modern.js
├── index.modern.js.map
├── lib
│   ├── altpayment
│   ├── assets
│   ├── components
│   ├── tests
│   ├── themes
│   └── util
└── src
    ├── App.d.ts
    └── main.d.ts

... not having a react/dist/react folder there.

Also, I added a new github action to check that, so that should be automatic from now on.