Add the RevenueCat Customer Center (self service subscription management UI) to an app. Use when the user asks to add a customer center, build a self service subscriptions screen, let users manage subscriptions in app, add a subscription management screen, present CustomerCenterView, call presentCustomerCenter, or wire a 'manage subscription' button to the RevenueCat customer center on iOS, Android, Kotlin Multiplatform, Flutter, or React Native.