[Vertex AI] Add AppCheck, Auth and Storage frameworks to sample

[andrewheard]

• Added the FirebaseAppCheck, FirebaseAuth and FirebaseStorage frameworks to the sample app to make it easier for devs to try out related features.
• Added a placeholder AppCheckProviderFactory that returns a simple AppCheckNotConfigured error since AppCheckDebugProviderFactory and DeviceCheckProviderFactory are very noisy with -FIRDebugEnabled (if App Check is not configured on the Firebase app -- the more common situation for sample users).
• Switched from configuring Firebase in init() to a UIApplicationDelegate to silence a [GoogleUtilities/AppDelegateSwizzler][I-SWZ001014] App Delegate does not conform to UIApplicationDelegate protocol. warning with -FIRDebugEnabled.

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