[Toolkit] Add support for documenting props API

[Kocal]

Maybe something similar to https://github.com/smnandre/ux-kit-bootstrap/blob/743023df35fa8b4925f115c76d36dc869cbca4dc/bootstrap/templates/components/Carousel.html.twig#L1-L23

Either in the same file, but we need to introduce some parsing first in order to validate them (and use them in the UX website on component documentation page), either we simply put them in the *.meta.json files (that's the easiest solution for the moment)