Docs: Vitest setup: Documentation for how to add vite-tsconfig-paths to support absolute paths in tests

[SanjoSolutions]

Goals

1. Documentation for how to setup vite-tsconfig-paths to support import aliases in test files.

Non-Goals

No response

Background

Some projects might have set-up a import alias like "@/*": ["./src/*"]. This is an option that is available when one creates a Next.js app with "create-next-app". To support imports with such import alias in test files it seems to be required to set up a solution like vite-tsconfig-paths. By providing documentation for how to configure this, it can potentially be made more straight forward to users to make this work (saving Googling and picking a solution).

Proposal

I suggest to add documentation for configuring vite-tsconfig-paths in the section https://nextjs.org/docs/app/building-your-application/testing/vitest#manual-setup.

[SanjoSolutions]

I have created a PR for this: #72430