[addon-centered] Peer dependencies

Describe the bug The @storybook/addon-centered package has the following peerDependencies:

{
  "peerDependencies": {
    "mithril": "*",
    "preact": "*",
    "react": "*"
  }
}

Meaning installing it will always add 2-3 annoying warnings to a project. You’ll never have more than 1 of those installed at the same time, and you can even use the addon without any of them.

Expected behavior A package should not have peerDependencies that can’t/won’t ever be met. Please find a better solution (optionalDependencies?), or just remove the peerDependencies all together in this case.

[shilman]

Hey @leoyli here you go go go!! 🚀

[leoyli]

@Svish, yes fixed, stay tune 👀