Enable Storybook on-demand mode

[AlanGreene]

Changes

Instead of loading all stories on boot up, load stories on demand. This was broken in a previous release but appears to be working now in at least rc5 and later.

This produces faster loading times and significant improvements in bundles.

/kind misc

Submitter Checklist

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Release Notes

NONE

[AlanGreene]

/test tekton-dashboard-unit-tests

[briangleeson]

/lgtm

[tekton-robot]

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