[contrib/auth] Add `QueryClient.Roles()` method

[bounoable]

Allow querying of user roles:

package example

func example(client auth.QueryClient) {
  userID := uuid.New()
  roleIDs, roleNames, err := client.RolesOf(context.TODO(), userID)
}

[groggy7]

In which file i should implement such a method?

[bounoable]

This is the contrib/auth package. The QueryClient can be found in the contrib/auth/api.go 👍🏼