feat(731) migrate newskit demo to docs site

[mutebg]

closes #731

What

1. Background - migrate newskit demo from separate repo to newskit repo under docs folder
2. What did you do:

• Replaced legacy components like Stack, Grid, Card and AudioPlayer with GridLayout, CardComposable and AudioPlayerComposable in the code examples
• Updated demo template to use GridLayout and made it mobile friendly
• Added themes directly from the publisher instead of local ones.
• Update the fetch-fonts script to download the licensed fonts for storybook and docs.

3. What does the reviewers should expect -> go to http://ncu-newskit-docs-pr.s3-website-eu-west-1.amazonaws.com/731-add-demo/demo/ and checkout the demo.

I have done:

• Written unit tests against changes
• Written functional tests against the component and/or NewsKit site
• Updated relevant documentation

I have tested manually:

• The feature's functionality is working as expected on Chrome, Firefox, Safari and Edge
• The screen reader reads and flows through the elements as expected.
• There are no new errors in the browser console coming from this PR.
• When visual test is not added, it renders correctly on different browsers and mobile viewports (Safari, Firefox, small mobile viewport, tablet)
• The Playground feature is working as expected

Before:

After:

Who should review this PR:

How to test:

[pp-serviceaccount]

You can preview these changes on:
Documentation Site: http://ncu-newskit-docs-pr.s3-website-eu-west-1.amazonaws.com/731-add-demo
Storybook: http://ncu-newskit-docs-pr.s3-website-eu-west-1.amazonaws.com/731-add-demo/storybook

[jps]

I get an issue with the fonts because I'm in the dark theme, also there is no way to change out of it, not sure if this is something we want to fix in this ticket though.

[Vanals]

LGTM, is the dw theme gonna be changed in this ticket?

Also in a follow up ticket we could add the font metrics, for proper TextCropping, and I was wondering if we have a video of the DEMO? like someone running over it? Would be nice if we could include it in the home pace

[mutebg]

LGTM, is the dw theme gonna be changed in this ticket?

I am waiting for newscorp-ghfb/newskit-themes-publisher#108 so that I can add the rest of the themes

[JohnTParsons]

Nice work, Stoyan