[v4] Allow customizing Lightning CSS in @tailwindcss/postcss

[cossssmin]

Would be super useful if we could pass Lightning CSS options to the PostCSS plugin.

Looking at the types and source, looks like we can only toggle minification:

type PluginOptions = {
    base?: string;
    optimize?: boolean | {
        minify?: boolean;
    };
};

Would be useful if we could define targets or include/exclude for example 👍