DQN eval_epsilon overwrite with epsilon on 0.0

Hi Acme team, I think JAX DQN might set the evaluation epsilon to the exploration epsilon if deterministic evaluation is requested (eps=0.0, [here](https://github.com/deepmind/acme/blob/860dbab686042573569b84223d8da6d43d09c304/acme/agents/jax/dqn/builder.py#L183)). Replacing this with `self._config.eval_epsilon is not None` fixed it for me - does this also occur on your end?

Thanks so much for checking!