Add `@testing-library/vue` for integration tests

[jsulpis]

I would like to use Testing Library for integration tests, but currently there are issues with nuxt 3 auto-imports and I did not manage to finish the setup the way I want.

I managed to have a working integration test for a simple component using the nuxt-vitest module, but for more complex components I still had issues with things that are globally injected, like $t(...) in templates for translations.

I will try again once nuxt-vitest is a bit more mature.