Rename add-ons to apps in Supervisor API

[agners]

Description

The user facing rename of add-ons to apps is largely done.

To avoid confusion in the future, ideally we also rename add-ons to apps in our code base. In a first step the public facing API should be adjusted. Supervisor definitly needs to keep backwards compatible, but we can introduce the new endpoints alongside the existing ones (/apps alongside /addons).

Since this is a rather big change an API versioning might be appropriate for this.

Additional context

No response