Proof of concept: support storybook middleware

[tadhglewis]

The problem: I need a api endpoint to generate auth tokens for local development. With sku I can simply use dev server middleware however this isn't possible when running storybook.

Storybook actually supports a router middleware since 2016 however it isn't currently documented as per storybookjs/storybook#15300 (comment) so it
might be debatable whether we want to support it in sku.

There is probably a larger discussion to be had around a better implementation for storybook as configuring storybook through .storybook/* directory isn't supported in sku projects - talked to @askoufis here

Todo

• fix broken tests
• check if this is something we should actually support
• make sure it won't break existing storybook projects

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[tadhglewis]

Closing in favor of supporting supporting config dir or dangerously override