Refactor configs to have env in seperate yaml + Fix training

lerobot/configs/env/pusht.yaml

@@ -0,0 +1,25 @@
+# @package _global_
+
+hydra:
+  job:
+    name: pusht
+
+eval_episodes: 50
+eval_freq: 7500
+save_freq: 75000
+train_steps: 50000  # TODO: same as simxarm, need to adjust
+
+fps: 10
+
+env:
+  name: pusht
+  task: pusht
+  from_pixels: True
+  pixels_only: False
+  image_size: 96
+  action_repeat: 1
+  episode_length: 300
+
+policy:
+  state_dim: 2
+  action_dim: 2

lerobot/configs/env/simxarm.yaml

@@ -0,0 +1,26 @@
+# @package _global_
+
+hydra:
+  job:
+    name: simxarm
+
+eval_episodes: 20
+eval_freq: 1000
+save_freq: 10000
+train_steps: 50000
+
+fps: 15
+
+env:
+  name: simxarm
+  task: lift
+  from_pixels: True
+  pixels_only: False
+  image_size: 84
+  action_repeat: 2
+  episode_length: 25
+  fps: ${fps}
+
+policy:
+  state_dim: 4
+  action_dim: 4