Add vue story indexer to support storyStoryv7

[tobiasdiez]

Similar to https://github.com/storybookjs/addon-svelte-csf/blob/ad8c44f6c7c64c1ab83be63f038456e0a5b6c30f/src/preset/index.js#L53-L61.

To test: remove storyStoreV7: false, in vite example

[JReinhold]

Let me know if you need any guidance @tobiasdiez. While @j3rem1e built the indexer for addon-svelte-csf, I've been looking through it quite a bit to understand how it works and what it needs to do.

[tobiasdiez]

Thanks for the offer @JReinhold. Taking the svelte code as an example, this was not too hard to implement. The only thing that is not clear to me is how to generate the story id. The current solution (file name + story name) works locally but chromatic has issues with it, see #38.