Add a web-types file for documenting component

[imagoiq]

Is your feature request related to a problem? Please describe.

It would be nice to ship with MJML library a web-types.json file documenting MJML component and attributes. Web-types is a de-facto standard way to declare HTML custom elements to IDE.

Additional context
Some IDE have a MJML plugin which declare such components, but it doesn't work in every situation (e.g. in my case when using MJML inside twig).