Addon-docs: Add fontFamily prop to Typeset component

[umar-ahmed]

Issue: #8161

What I did

• Added fontFamily prop to Typeset component that allows you to set the font family on the type sample
• Added a story for Typeset illustrating the use of the fontFamily prop

How to test

1. cd examples/official-storybook && yarn storybook
2. Search for font family
3. Verify that the font family story renders the type sample using a monospace font

• Is this testable with Jest or Chromatic screenshots? yes (not sure how to set that up though)
• Does this need a new example in the kitchen sink apps? not sure
• Does this need an update to the documentation? not sure

If your answer is yes to any of these, please make sure to include it in your PR.

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[shilman]

Awesome! LGTM!