Mixin for ViewSets that adds RBAC permission checks based on a class-level
rbac_permission_map dict mapping DRF actions to permission codes.

Usage::

class MyViewSet(RBACPermissionMixin, GenericViewSet):
    rbac_permission_map = {
        "create": "file.create",
        "list": "file.read",
        "retrieve": "file.read",
        "update": "file.update",
        "partial_update": "file.update",
        "destroy": "file.delete",
    }