Rename (with deprecation) controllers API and payload to access keys

[peterpeterparker]

Motivation

As we are going to expose guards and access keys related features for serverless developers, it's about time to clean-up the API and code to finalize the transition from "Controllers" to "Access Keys".

Let's make a breaking change in the DID files but keep the old endpoints as deprecated for a long time.

[peterpeterparker]

No rush. I can do it one of those days - i.e. if devs start using the end points directly, definitely makes sense but, as long that only the tooling does it - even if it's a bit weird naming wise - there is no rush.