[v4] Enhancement as a Custom language theme for code editor

[sasaorasanin]

Hello, I just watched your video with Nuno on filament 4 and maybe instead of adding support for requested languages for code editor, just add a custom theme option. In example, at some probject I wrote a validation language and used code mirror with custom theme for that language. Would be awesome to have that ability in filament. Can try to contribute if needed :D