Restructured the website repo to allow for future i18n and content translation

[sarahmaddox]

Preview: https://deploy-preview-1909--competent-brattain-de2d6d.netlify.app/

Fixes #1127

Notes:

• For a full description of what needs to be done for translation of the docs, see the product requirements doc: http://bit.ly/kubeflow-i18n
• I thought about moving the images into the /static/ directory so that we could share them across languages - but that would break the structure of the OWNERS files.
• After testing the redirects, I've discovered that the _redirects file needs to be in the language subdirectory. That is, for the English docs, the _redirects file must be in /en/.
• I've removed the Kubeflow customization of the logic to create the Edit this page URL, in the Docsy partial template at https://github.com/kubeflow/website/blob/master/layouts/partials/page-meta-links.html#L9. Now that Kubeflow has the /en/ directory, the Docsy logic should work. Note that it won't work until we've merged this PR. Click Edit this page on any page to see the URL constructed by the logic. Remove the /en part of the path to make the link work in the current directory structure (before this PR is merged).

[kubeflow-bot]

This change is 

[sarahmaddox]

/assign @joeliedtke
/assign @abhi-g
/assign @janeman98

This PR is now ready for review. Applying a hold to give us time for a careful review.
/hold

@janeman98 @joeliedtke @abhi-g Please would you take a look? See the PR description for preview link and more context.

[janeman98]

Thanks @sarahmaddox
Click Edit this page on any page to see the URL constructed by the logic. Remove the /en part of the path to make the link work in the current directory structure (before this PR is merged).

I am looking at the preview. May I know where to find Edit this page in the preview?

[sarahmaddox]

Hallo @janeman98, the link is at the top right of every page, in the same panel that shows the list of headings on the page. If you're using a small screen, the panel may not appear. Try reducing the zoom factor in your browser.

[janeman98]

Hallo @janeman98, the link is at the top right of every page, in the same panel that shows the list of headings on the page. If you're using a small screen, the panel may not appear. Try reducing the zoom factor in your browser.

Thanks @sarahmaddox ! I need to maximize my screen to see it. I am good now.

[janeman98]

I have randomly tested >40 pages in the preview. All worked as what mentioned above.

/lgtm

[abhi-g]

/lgtm

Thanks @sarahmaddox

[sarahmaddox]

/hold cancel

Thanks @abhi-g and @janeman98 - could you re-LGTM now that I've merged with master?

[abhi-g]

/lgtm

[sarahmaddox]

/approve

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