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)
• Create an enum on server to identify Mail and Calendar subscriptions