Code Insights: [FE] Update insight creation intro page designs and layouts
Created by: vovakulikov
Closes https://github.com/sourcegraph/sourcegraph/issues/28018
Context
Some parts of this page design still are under discussion so this PR may require some change around copy and small layout changes. But the main layout should stay the same.
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Important
This PR just updates the creation intro page design but doesn't add the capture group insight card component there. I will be done in a separate PR when we will be ready to activate capture group insight logic.