Fixes `net_arch` in `sb3_ppo_cfg.yaml` for Isaac-Lift-Cube-Franka-v0 task (#1249)

# Description
Two changes are made to fix _[Bug Report] sb3_ppo_cfg.yaml not work for
Isaac-Lift-Cube-Franka-v0 #1248_:

1. Add `sb3_cfg_entry_point` to
`source/extensions/omni.isaac.lab_tasks/omni/isaac/lab_tasks/manager_based/manipulation/lift/config/franka/init.py`
2. Change `net_arch=[32, 32, dict(pi=[256, 128, 64], vf=[256, 128,
64])]` to `net_arch=dict(pi=[256, 128, 64], vf=[256, 128, 64])` in line
19 of `sb3_ppo_cfg.yaml`.


Fixes #1248

## Type of change

- Bug fix (non-breaking change which fixes an issue)

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] My changes generate no new warnings

source/extensions/omni.isaac.lab_tasks/omni/isaac/lab_tasks/manager_based/manipulation/lift/config/franka/__init__.py

@@ -23,6 +23,7 @@ gym.register(
         "rsl_rl_cfg_entry_point": f"{agents.__name__}.rsl_rl_ppo_cfg:LiftCubePPORunnerCfg",
         "skrl_cfg_entry_point": f"{agents.__name__}:skrl_ppo_cfg.yaml",
         "rl_games_cfg_entry_point": f"{agents.__name__}:rl_games_ppo_cfg.yaml",
+        "sb3_cfg_entry_point": f"{agents.__name__}:sb3_ppo_cfg.yaml",
     },
     disable_env_checker=True,
 )
@@ -35,6 +36,7 @@ gym.register(
         "rsl_rl_cfg_entry_point": f"{agents.__name__}.rsl_rl_ppo_cfg:LiftCubePPORunnerCfg",
         "skrl_cfg_entry_point": f"{agents.__name__}:skrl_ppo_cfg.yaml",
         "rl_games_cfg_entry_point": f"{agents.__name__}:rl_games_ppo_cfg.yaml",
+        "sb3_cfg_entry_point": f"{agents.__name__}:sb3_ppo_cfg.yaml",
     },
     disable_env_checker=True,
 )

source/extensions/omni.isaac.lab_tasks/omni/isaac/lab_tasks/manager_based/manipulation/lift/config/franka/agents/sb3_ppo_cfg.yaml

@@ -16,7 +16,7 @@ learning_rate: !!float 3e-4
 clip_range: 0.2
 policy_kwargs: "dict(
                   activation_fn=nn.ELU,
-                  net_arch=[32, 32, dict(pi=[256, 128, 64], vf=[256, 128, 64])]
+                  net_arch=dict(pi=[256, 128, 64], vf=[256, 128, 64])
                 )"
 target_kl: 0.01
 max_grad_norm: 1.0