ability to set default addon tab per stories module

[jayarjo]

Would be great to have a way to set default addon panel. For some stories actions to be default, for others it'd better be controls, and then there might be several additional addons enabled too.

Something like activeAddonTab as one of the options in default export would do.

[shilman]

It looks like such a thing already exists:

https://github.com/storybookjs/storybook/blob/next/examples/official-storybook/stories/addon-a11y/base-button.stories.js#L10-L12

[jayarjo]

Awesome!