Presets - Add "addons" and "config" to preset extensions

[igor-dv]

I've played a bit with presets and realized that having more granular extensions for addons and config will be very helpful for creating presets.

For example, we can expose our addons as presets, i.e. using them like this:

// presets.js (or a future storybook.config.js)
[
  `@storybook/addon-vieports/preset`
]

// or with default params
[
  name: `@storybook/addon-vieports/preset`,
  options: { /* whatever this addon needs */ }
]

Same thing with a config.js file. Today we enforce people to create config.js in order to call the configure(loadStories, module);

We can create a preset that does it. One may use require.context or some other techniques.