add task progress prediction to N1.5

[youliangtan]

This adds the capability to predict action.task_progress with 0.0 to 1.0

0.0 = start of the episode
1.0 = end of the episode

This can be enabled by adding an extra key to the action_keys in data_config

an example is:

```py
class RobotDataConfig(BaseDataConfig):
    action_keys = [
        "action.left_arm",
        "action.right_arm",
        "action.left_hand",
        "action.right_hand",
        "action.waist",
        "action.base_height_command",
        "action.navigate_command",
        "action.task_progress",    <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< THIS
    ]