Add RTK Query example with Vitest configuration

[oidualc]

Resolves #3254

This pull request adds an example of RTK Query using Vite and testing it with Vitest.
More specifically it's a variation of the basic example.

All the other examples of RTK Query currently are built using Create React App. Since CRA does a lot of configurations under the hood, generally speaking tests with RTK Query using MSW to mock data work out of the box.
Vitest doesn't come with the same configurations and needs some manual setup that I couldn't find documented anywhere.

I hope this example will turn out to be useful for anybody who is using this stack and has trouble with the setup.

[codesandbox]

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