Provide types for `launch-editor-middleware`

[FloEdelmann]

Webpack can be configured using TypeScript configuration files: https://webpack.js.org/configuration/configuration-languages/

Using launch-editor-middleware in a TypeScript file however causes a "missing declaration file" error because there are no types bundled in the package. Also @types/launch-editor-middleware does not exist.

Would it be possible to add and bundle the types in the package?