allow passing function under config.plugins

[zanona]

Perhaps there's an alternative way of dealing with this kind of scenario, but for those who are interested in keeping their dependency graph updated, wouldn't it be a good idea to allow snowpack.config.js to also receive an array of functions as value for the plugins property, like so:

import postcss from "@snowpack/plugin-postcss";
import reactRefresh from "@snowpack/plugin-react-refresh";

/** @type { import("snowpack").SnowpackConfig } */
const config = {
	plugins: [postcss, reactRefresh],
	optimize: {
		bundle: true,
		minify: true,
		treeshake: true,
		target: "es2018",
	},
};

export default config;

This way the dependency graph would clear indicate those as:

instead of:

Additionally, this could be beneficial for those interested in quickly mocking a plugin behaviour or having small plugins which only make sense to the project without having to create a package for it and declare everything inline.