DOP-6197: add ref/hash behavior

[seungpark]

Stories/Links:

DOP-6197

Current Behavior:

This link contains a ref hash id (test in incognito window or clear local storage)
http://mongodb.com/docs/atlas/atlas-search/tutorial/#create-the--index.-18
This does not lead users to any significant portion of the page, just makes default selections.

Staging Links:

This staging link takes users to the correct selections and to the ref on the page:
https://deploy-preview-1563--docs-frontend-stg.netlify.app/docs/atlas/atlas-search/tutorial/#create-the--index.-18

Notes:

• This behavior is done by memoizing all the hashes included in each composable content at build time, and verifying if the hash in URL belongs to a selected content.
• In the case that multiple composable content have the same ref, this is a content issue and will result in the first composable content being returned.

README updates

• • This PR introduces changes that should be reflected in the README, and I have made those updates.
• • This PR does not introduce changes that should be reflected in the README

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[biancalaube]

LGTM! one small NiT