Update dirDecorator to pass script and dir to storybook function

[ghost]

Contributes to #508

Overall change: Update dirDecorator to pass script and dir to storybook function.

Code changes:

• Passed dir and script to storybook function to allow them to be used in components i.e.

addDecorator(dirDecorator)
.add('Timestamp', ({ script }) => (
  <Timestamp script={script} /* other props *//>
)

---

• I have assigned myself to this PR and the corresponding issues
• Tests added for new features
• Test engineer approval

[j-pendlebury]

Looks good to me

[jamesbrumpton]

LGTM. Happy for this to be merged.