[#79] Updated markup and prop for Promo component to be Contained or not.

[joshua-salsadigital]

Checklist before requesting a review

closes #79

• I have formatted the subject to include the issue number
  as [#123] Verb in past tense with a period at the end.
• I have provided information in the Changed section about WHY something was
  done if this was a bespoke implementation.
• I have performed a self-review of my code.
• I have commented on my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• I have run new and existing relevant tests locally with my changes,
  and they have passed.
• I have provided screenshots, where applicable.

Changed

1. Updated the markup to use the same approach as what Basic component uses - containment
2. Added props to the Storybook story ( Contained & With background)

Screenshots