Added UMP SDK integration to Interstitial sample

[malandr2]

Description

Added UMP SDK integration to Interstitial sample

• Created consent_manager.dart class to handle all the consent work
• Calling requestConsentInfoUpdate on every app launch.
• Pause/Resume timer when consent form is on screen
• Added a privacy settings button which shown/hidden based on privacyOptionsRequirementStatus
• Not initializing the Mobile SDK until canRequestAds returns true

Related Issues

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