Renaming GOAL to GOAL_SIGNAL

ml-agents/mlagents/trainers/tests/simple_test_envs.py

                     obs_spec[i] = ObservationSpec(
                         shape=obs_spec[i].shape,
                         dimension_property=obs_spec[i].dimension_property,
-                        observation_type=ObservationType.GOAL,
+                        observation_type=ObservationType.GOAL_SIGNAL,
                         name=obs_spec[i].name,
                     )
         return obs_spec

ml-agents/mlagents/trainers/torch/networks.py

         self._total_goal_enc_size = 0
         self._goal_processor_indices: List[int] = []
         for i in range(len(observation_specs)):
-            if observation_specs[i].observation_type == ObservationType.GOAL:
+            if observation_specs[i].observation_type == ObservationType.GOAL_SIGNAL:
                 self._total_goal_enc_size += self.embedding_sizes[i]
                 self._goal_processor_indices.append(i)