Adds flag to preserve joint order inside `JointActionCfg` action term (#787)

# Description

Adds the attribute `preserve_order` in `JointActionCfg`, to choose whether joint-related actions should keep the same
order as how the `joint_names` are listed in the config.

Fixes #786

## Type of change

- New feature 

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [x] I have updated the changelog and the corresponding version in the
extension's config/extension.toml file
- [x] I have added my name to the CONTRIBUTORS.md or my name already
exists there

CONTRIBUTORS.md

@@ -54,6 +54,7 @@ Guidelines for modifications:
 * Rosario Scalise
 * Shafeef Omar
 * Vladimir Fokow
+* Xavier Nal
 * Zhengyu Zhang
 * Ziqi Fan
 

source/extensions/omni.isaac.lab/config/extension.toml

 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.21.0"
+version = "0.21.1"
 
 # Description
 title = "Isaac Lab framework for Robot Learning"

source/extensions/omni.isaac.lab/docs/CHANGELOG.rst

 Changelog
 ---------
 
+0.21.1 (2024-08-06)
+~~~~~~~~~~~~~~~~~~~
+
+* Added a flag to preserve joint ordering inside the :class:`omni.isaac.lab.envs.mdp.JointAction` action term.
+
+
 0.21.0 (2024-08-05)
 ~~~~~~~~~~~~~~~~~~~
 

source/extensions/omni.isaac.lab/omni/isaac/lab/envs/mdp/actions/actions_cfg.py

@@ -29,6 +29,8 @@ class JointActionCfg(ActionTermCfg):
     """Scale factor for the action (float or dict of regex expressions). Defaults to 1.0."""
     offset: float | dict[str, float] = 0.0
     """Offset factor for the action (float or dict of regex expressions). Defaults to 0.0."""
+    preserve_order: bool = False
+    """Whether to preserve the order of the joint names in the action output. Defaults to False."""
 
 
 @configclass

source/extensions/omni.isaac.lab/omni/isaac/lab/envs/mdp/actions/joint_actions.py

@@ -56,7 +56,9 @@ class JointAction(ActionTerm):
         super().__init__(cfg, env)
 
         # resolve the joints over which the action term is applied
-        self._joint_ids, self._joint_names = self._asset.find_joints(self.cfg.joint_names)
+        self._joint_ids, self._joint_names = self._asset.find_joints(
+            self.cfg.joint_names, preserve_order=self.cfg.preserve_order
+        )
         self._num_joints = len(self._joint_ids)
         # log the resolved joint names for debugging
         carb.log_info(