Implementation of gradient button

[Emibergo02]

Gradients are the only thing missing right now.
It would be breaking change to the website and for every plugin that uses the web editor API to format text

I saw many people use https://www.birdflop.com/resources/rgb/ for gradients but it is not an official solution

[zml2008]

Hm? MiniMessage has <gradient> which works perfectly fine from the webui. There's not a button for it, but that starts getting into the weeds of how to best provide a ui for tags that accept arguments -- do we want modal dialogs? or just have users enter them manually