Update Jest config with SWC docs

[nvh95]

Motivation/ Context

• When upgrading next from 11 to 12, I followed Upgrade guide from 11 => 12. I removed .babelrc to opt-in SWC. I thought that's all, but after removing .babelrc, Jest broke immediately. So I follow the guide https://nextjs.org/docs/advanced-features/compiler#jest to configure Jest to work with SWC. I copied the content of jest.config.js to my project but it does not work. The reason:

-const createJestConfig = nextJest({ dir }) // `dir` IS NOT DEFINED
+const createJestConfig = nextJest({ dir: './' }) // Should change to this. Sync with https://nextjs.org/docs/testing#setting-up-jest-with-the-rust-compiler

• This PR is to help others to configure Jest with SWC by copying code from the documentation site without encountering the same issue as I did.

Documentation

• Update the docs so users can just copy and paste when configuring Jest with SWC (Sync with https://nextjs.org/docs/testing#setting-up-jest-with-the-rust-compiler)
• Make sure the linting passes by running pnpm lint
• The examples guidelines are followed from our contributing doc

Future work

• Since Upgrade guide from 11 => 12 did not mention anything about Jest. If I remove .babelrc to opt-in SWC. The current Jest settings will crash (since it's using babel). We likely want to update the Upgrade guide to mention this cc: @leerob

[balazsorban44]

Thanks!