[v2] Remove master level key in favor of jwt tokens only

As discussed internally, we should remove the master level key that's able to access all the management APIs for the function app in favor of only supporting short lived jwt tokens.

Start by locating how the function app handles the master-level key and authentication for management APIs. Determine the intended short-lived JWT-only flow and identify the affected tests or entry points; done means the master key no longer grants access and JWT authentication remains functional.

Written by the indexing model from the issue text.