Sources needs to be able to check if the user is authorized to perform the operations by using Kessel instead of RBAC.

The goal is to have an environment variable that allows us switching the authorization back end easily.

Relevant code: https://github.com/RedHatInsights/sources-api-go/blob/f7349490437b769ec3cdbf160101f6311cae5ac2/middleware/authorization.go#L93