Snapshot, diff, and apply for roles and permissions

Summary Similar to the excellent schema management endpoints, there should be a way to manage roles and permissions. This is similar in spirit but not implementation to Basic Example Three new API endpoints, similar in operation to the existing /schema/* APIs. access-control might not be the best name but this is the idea: • GET /access-control/snapshot - Retreive a snapshot of the access controls, including roles and permissions • POST /access-control/diff - Retrieve the diff between the posted snapshot and the current access controls • POST /access-control/apply - Apply the posted diff This will allow programmatic management of access control across Directus instances, removing the need for human interaction to build applications across different environments, and make it possible to store access control configuration in source control as a JSON file, alongside the schema JSON. Motivation We want to create Directus applications in a repeatable fash…