Why jaco_arm/joints_pos shape is (1, 6, 2) and how to do joint position control?

@yuvaltassa @kevinzakka

Hi `dm_control` developers team,

As the title suggested, I have 2 questions:

1. For the default manipulation env with kinova jaco arm, why the joint position has 2 dim for each joint for a 6-DoF jaco arm? How to convert this observation to `qpos`, which has exactly 1 dim per joint?

2. For the same env, how to turn the torque control to joint position control (control `qpos`)?

The minimum code is:

```python
import gymnasium as gym
env = gym.make("dm_control/lift_large_box_features-v0", render_mode="rgb_array")
print(env.observation_spec())
print(env.action_spec())
```

and this gives me:

```shell
env.observation_spec(): OrderedDict([
('jaco_arm/joints_pos', Array(shape=(1, 6, 2), dtype=dtype('float64'), name='jaco_arm/joints_pos')),
('jaco_arm/joints_torque', Array(shape=(1, 6), dtype=dtype('float64'), name='jaco_arm/joints_torque')),
('jaco_arm/joints_vel', Array(shape=(1, 6), dtype=dtype('float64'), name='jaco_arm/joints_vel')),
('jaco_arm/jaco_hand/joints_pos', Array(shape=(1, 3), dtype=dtype('float64'), name='jaco_arm/jaco_hand/joints_pos')),
('jaco_arm/jaco_hand/joints_vel', Array(shape=(1, 3), dtype=dtype('float64'), name='jaco_arm/jaco_hand/joints_vel')),
('jaco_arm/jaco_hand/pinch_site_pos', Array(shape=(1, 3), dtype=dtype('float64'), name='jaco_arm/jaco_hand/pinch_site_pos')),
('jaco_arm/jaco_hand/pinch_site_rmat', Array(shape=(1, 9), dtype=dtype('float64'), name='jaco_arm/jaco_hand/pinch_site_rmat')),
('unnamed_model/angular_velocity', Array(shape=(1, 3), dtype=dtype('float64'), name='unnamed_model/angular_velocity')),
('unnamed_model/linear_velocity', Array(shape=(1, 3), dtype=dtype('float64'), name='unnamed_model/linear_velocity')),
('unnamed_model/orientation', Array(shape=(1, 4), dtype=dtype('float64'), name='unnamed_model/orientation')),
('unnamed_model/position', Array(shape=(1, 3), dtype=dtype('float64'), name='unnamed_model/position')),
])

env.action_spec(): (
BoundedArray(shape=(9,), dtype=dtype('float64'), name='jaco_arm/joint_1\tjaco_arm/joint_2\tjaco_arm/joint_3\tjac
o_arm/joint_4\tjaco_arm/joint_5\tjaco_arm/joint_6\tjaco_arm/jaco_hand/finger_1\tjaco_arm/jaco_hand/finger_2\tjac
o_arm/jaco_hand/finger_3', minimum=[-0.62831853 -0.62831853 -0.62831853 -0.83775804 -0.83775804 -0.83775804
-5. -5. -5. ], maximum=[0.62831853 0.62831853 0.62831853 0.83775804 0.83775804
0.83775804
5. 5. 5. ])

```

by processing info from above we have:

```shell
('jaco_arm/joints_pos', Array(shape=(1, 6, 2), dtype=dtype('float64'), name='jaco_arm/joints_pos')),
```

And I just wonder why it's (1, 6, 2).