Add Organization Isolation blueprint

What does this MR do and why?

See the epic &11670 and the past investigation done in #394800 (closed)

Review app: https://main-ee-133796.docs.gitlab-review.app/ee/architecture/blueprints/organization/isolation.html

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Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

MR acceptance checklist

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