Add Application permission to support AppCatalog.ReadWrite.All
According to https://docs.microsoft.com/en-us/graph/api/resources/teamsapp?view=graph-rest-beta, only delegated permission is supported to manipulate Teams AppCatalog which means a sign-in user is needed when taking use of those APIs. However, the Application permission can provide the ability to make related actions more automatically and support more meaningful and realistic use-cases.
For example, my use-case is to provided an application to automatically install a new Bot, created in Azure, to Teams. So I really think the Application permission is needed.