[FE Offline Transfer] 1. Scaffold Vue App and basic routes
Scaffold the base for mounting the new app for Offline Transfer.
* Register route, eg offline-transfer
* Mount empty Vue app
* Determine whether we _need_ to use to haml at all https://docs.gitlab.com/development/fe_guide/vue/#providing-data-from-haml-to-javascript
* Determine where the code should live. It will not be restricted to enterprise
* ~~Should the code be stored in EE folder? If its premium and ultimate, put frontend in EE, and use license check~~
* Create feature flag `offline_transfer_ui `and use
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