feat: add get_role action to Authorization domain

Add get_role action for retrieving single role by ID through
code interface.

lib/mv/authorization/authorization.ex

@@ -23,6 +23,7 @@ defmodule Mv.Authorization do
     resource Mv.Authorization.Role do
       define :create_role, action: :create_role
       define :list_roles, action: :read
+      define :get_role, action: :read, get_by: [:id]
       define :update_role, action: :update_role
       define :destroy_role, action: :destroy
     end