Option to prevent fetch story

[didkan]

Problem
Whenever you use the StoryblokMixin.ts it will try and fetch a story for the current url.
We are using the mixin in a header component on our site.
This result in a http request with 404 result for every page on our site.
If you want to use the StoryblokMixin.ts without this undesired behavior we need to be able to tell it not to.

Solution
Added a data property storyblok.fetchStory (default true) that will control if a story should be fetched or not. When using the mixin in a component, just add this property set to false to prevent the fetch:

data () {
  return {
    storyblok: {
      fetchStory: false
    }
  }
}