💄 Introduce storybook addon for vue-slots

[langehm]

Is your feature request related to a problem? Please describe.
Writing stories with complex slots is laborious and only possible via writing the whole template itself.

Describe the solution you'd like
An addon exists for storybook, to solve this: https://storybook.js.org/addons/storybook-addon-vue-slots

Introduce this addon and transform all existing stories to the new syntax indruced with this addon.

[langehm]

Before introducing this addon we need to check if this covers all our needs regarding slots. There are some open issues ...

[langehm]

The current version of this addon is sadly depending on storybook version 7.x.x 😢
The Version 0.9.30-next.2 would be compatible ...