Move parallel_network flag from algorithm to network (#911)

alf/algorithms/ddpg_algorithm.py

alf/algorithms/ddpg_algorithm_test.py

alf/algorithms/sac_algorithm.py

alf/algorithms/sac_algorithm_test.py

alf/algorithms/sarsa_algorithm.py

alf/examples/ddpg_fetchreach.gin

alf/examples/ddpg_pendulum.gin

alf/examples/her_target_navigation_states.gin

alf/examples/sac_actrepeat_fetch/sac_actrepeat_fetch.gin

alf/examples/sac_carla_conf.py

alf/examples/sac_fetchreach.gin

alf/examples/sac_humanoid.gin

alf/examples/sac_lagrw_cargoal1_conf.py

alf/examples/sarsa_sac_mujoco.gin

alf/networks/critic_networks.py

alf/networks/q_networks.py