Add grasp critic

- Implemented grasp critic to evaluate gripper actions
- Added corresponding config parameters for tuning

lerobot/common/policies/sac/configuration_sac.py

@@ -42,6 +42,14 @@ class CriticNetworkConfig:
     final_activation: str | None = None
 
 
+@dataclass
+class GraspCriticNetworkConfig:
+    hidden_dims: list[int] = field(default_factory=lambda: [256, 256])
+    activate_final: bool = True
+    final_activation: str | None = None
+    output_dim: int = 3
+
+
 @dataclass
 class ActorNetworkConfig:
     hidden_dims: list[int] = field(default_factory=lambda: [256, 256])