Add gym-aloha, rename simxarm -> xarm, refactor

lerobot/configs/env/xarm.yaml

@@ -0,0 +1,28 @@
+# @package _global_
+
+eval_episodes: 20
+eval_freq: 1000
+save_freq: 10000
+log_freq: 50
+offline_steps: 25000
+online_steps: 25000
+
+fps: 15
+
+dataset_id: xarm_lift_medium
+
+env:
+  name: xarm
+  handle: XarmLift-v0
+  # TODO(aliberts): replace task with handle
+  task: lift
+  from_pixels: True
+  pixels_only: False
+  image_size: 84
+  # action_repeat: 2  # we can remove if policy has n_action_steps=2
+  episode_length: 25
+  fps: ${fps}
+
+policy:
+  state_dim: 4
+  action_dim: 4