IAP - Add In-App-Purchase stuff

[mfreeman451]

https://pub.dev/packages/in_app_purchase
https://console.firebase.google.com/u/0/project/chaseapp-8459b/extensions/instances/firestore-revenuecat-purchases?tab=usage

so somewhere in the app, profile or something, users should see a button similar to this:

Also, on app load, users should be shown a screen like this, and once they close it, it does not reappear:

Replace "Ocean Journal" with "ChaseApp Premium"

• RevenueCat integration #246
• Update flutter
• Configure Apple - https://developer.apple.com/in-app-purchase/
• https://appstoreconnect.apple.com/apps/1462719760/appstore/promotions
• AppStore Connect updates https://appstoreconnect.apple.com/apps/1462719760/appstore/subscriptions
• Configure Android - https://developer.android.com/google/play/billing/getting-ready
• Update back-end
• To add in-app products, you need to add the BILLING permission to your APK

[rutvik110]

#247