Redirect / Take down deprecated whitepaper landing page

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This page still exists on the website, but we've removed the whitepaper that it links to: https://sourcegraph.com/resources/a-lp-how-sourcegraph-ai-platform-powers-cody

We'll need to remove that landing page as well.

Redirect the following two pages:

• https://sourcegraph.com/whitepaper/how-sourcegraph-ai-platform-powers-cody.pdf
• https://sourcegraph.com/resources/a-lp-how-sourcegraph-ai-platform-powers-cody

to
https://sourcegraph.com/blog/how-cody-understands-your-codebase

cc @chris.sev

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WEB-123 Take down deprecated whitepaper landing page