Fix nextjs-keystone example deploy to Vercel

[borisno2]

Fixes #8430

The Deploy to Vercel button for the nextjs-keystone example just clones that one folder and therefore when deployed does not have access to files outside that directory. To simplify the solution this PR just sets the prismaClientPath in the config directly instead of importing example-utils.ts

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Latest commit: 4332f65

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