Refactor Tanuki Bot test suite

What does this MR do and why?

Since we re-organized the chat duo files due to siderail we had this test file named wrong. This MR is fixing it.

All test from app_spec.js are moved to duo_chat_classic_spec.js. app_spec.js file contains tests related to tanuki/app.vue

References

related to: https://gitlab.com/gitlab-org/gitlab/-/issues/577807+

Screenshots or screen recordings

no visual change

How to set up and validate locally

1. run test locally using

   yarn jest ee/spec/frontend/ai/tanuki_bot/components/app_spec.js ee/spec/frontend/ai/tanuki_bot/components/duo_chat_spec.js
   

MR acceptance checklist

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