Add AppStore subscription to Calendar App

[murilopereirame]

As a Tuta Calendar user, I want to subscribe to a plan using in-app subscription as my Payment method

AC

• Users are able to subscribe on calendar app using AppStore in app subscription
• Subscriptions made on Tuta Mail are valid on Tuta Calendar
• User can't manage a subscription made on Tuta Mail inside Tuta Calendar
• When trying to manage a subscription made within other Tuta App, a message appear informing user to manage on AppStore or inside the other app.

Tasks

• Add the respective subscriptions on AppStore connect to Calendar App
• Update backend to handle calendar subscriptions
• Detect subscriptions made within Mail App (and the opposite)
  • Check which app was used to subscribe
  • Update model to hold this info
• Create an enum on server to identify Mail and Calendar subscriptions

Test notes (You may want to grab a snack for this)

Calendar App

• Verify that App Store payment is the only option on iOS (you should automatically select it).
• Verify that App Store payment is unavailable on Android, web, and desktop.
• Sign up for a paid account using App Store in Euros. Verify this works and that the prices are displayed correctly.
• Sign up for a paid account using App Store in some other currency (USD, BRL, GBP, etc.). Verify this works and that the prices are displayed correctly.
• Sign up for a free account, then switch to App Store payment. Verify this works.
• Sign up for a paid account using PayPal, then try to switch to App Store without canceling. Verify this does not work.
  • Cancel the subscription, and then try to switch to App Store. Verify this works.
• Change an App Store subscription from Revolutionary to Legend. Verify this works and that this is near-instant (should switch within a minute).
• Change an App Store subscription from Legend to Revolutionary. Verify this works, but the switch does not occur until the subscription renews.
• Verify that App Store subscriptions cannot be altered directly on any non-iOS app. You are redirected to the iTunes store.
• Try to delete your account with an App Store subscription. Verify you cannot do that.
  • Deleting from Settings -> Global settings -> Delete account
  • Deleting using Terminate Account
• Create some calendars and subscribe to external calendars
• Cancel a subscription. Once the subscription has expired, manually run the App Store Subscriptions batch job. Verify the account has no custom calendars.
• You can't manage your subscription created on the Mail App
  • You're prompted to open Mail App
• Create a subscription on Mail App
  • Let it expires
  • Run the batch job with a future date (Next day)
  • Change it on calendar app, you can pick another plan or resubscribe through Calendar App using App Store payments

Mail App

• Subscription with App Store payment still working
• You can manage subscriptions created on Mail App
• You can't manage your subscription created on the Calendar App
  • You're prompted to open Calendar App
• Create a subscription on Calendar App
  • Let it expires
  • Run the batch job with a future date (Next day)
  • Change it on mail app, you can pick another plan or resubscribe through Mail App using App Store payments

[murilopereirame]

• The batch job isn't deleting the calendars
• App Store subscription dialog is being shown for users while subscribed with another payment method