Add class name support

[andrewmurphyio]

Adds a new feature for adding custom classnames

[AdrianMaj]

That won't work, + I don't have access to push to your branch. I am not sure if $patchStyleText will work with className (probably not), also converters are not updated to handle this, and client feature is not exported. I will take a deep look to it later and fix it, anyway thanks for PR!

[andrewmurphyio]

I struggled to get this working locally because of payload versioning issues. If you don't have time to finish it off maybe you can help me finish it?

[AdrianMaj]

What payload versioning issues? The simplest way to run this locally (that's how I do it) is to hit pnpm build on the plugin project, and then on any payload project pnpm install "file:../path/to/plugin-root, then it should work like a normal package from npm. Not sure if you have to add it manually to package.json with the name for first time and then just install it again when updated and builded.

At the moment my free time is limited, so I would be grateful if you want to finish it, otherwise I will do it in my spare time. If you need any help feel free to ask, thanks!