IMPROVE - Connect `WelcomeView` and `WelcomeViewAddVehicle` to App Flow

[mikaelacaron]

Describe the feature you want to improve

• WelcomeView and WelcomeViewAddVehicle have been created but aren't officially attached to the actual app flow.
• Connect these two screens so that a user using the app for the first time will see the WelcomeView, and then push WelcomeViewAddVehicle after tapping continue
• Change the "Welcome 🥳 " button to say "Add Vehicle"
• Once Add Vehicle is tapped, dismiss this onboarding flow, and the user should see the DashboardView

[!NOTE] Don't actually write the code for adding the vehicle in Firebase, because I want to look closer at how this works (this is going to be broken in a different task), because the functionality is in the SettingsViewModel, which isn't accessible at this point)

Describe alternatives you've considered

N/A