[Storybook] Notify the user about stories that use the mock-api

[larsvanbraam]

Introduction

So on one of my projects we use the mock-API in multiple components, since Storybook doesn't start up the mock server by default we might end up with stories that appear broken because of XHR requests failing.

Suggestion

To avoid the stories from being broken we basically have two options:

1. Always enable the mock-API when starting up Storybook so all stories work like expected.
2. Gracefully let the user know when a story requires the mock-API to be enabled.

The first option is probably the easiest to implement but it also has a downside because always running the mock-API causes extra processes to be started that might slow down the stories that do not require the mock-API.

The second option might be better for performance but also requires users to mark stories as API-dependant and would require some form of UI that instructs users to start up Storybook with the mock-API enabled.