Fetch root config when version doesn't have one

[mshaaban088]

If I have a directory structure like this

.
├── static
│   ├── manager.c2ca3b28e7a25aae27ab.bundle.js
│   └── preview.c03632fa3b30af3d9784.bundle.js
├── v1
│   ├── static
│   ├── favicon.ico
│   ├── iframe.html
│   └── index.html
├── v2
│   ├── static
│   ├── favicon.ico
│   ├── iframe.html
│   └── index.html
├── v3
│   ├── static
│   ├── favicon.ico
│   ├── iframe.html
│   └── index.html
├── favicon.ico
├── iframe.html
├── index.html
└── storybook-config.json

You should safely assume that there will be one storybook-config.json file stored in the root directory where you see all available-versions and other configs. IMHO this file shouldn't be redundant in every version.

The issue is, with the current implementation, in each version, the addon tries to load the storybook-config.json in that version, and if it is not there, it will reject the promise, that's based on fetch specifications, it will always return a promise that resolves to a Response object (ok will be false in case of 404), but we should instead load the config file from the root directory, and that's basically what I did.