# Description

This MR merges all the refactorings done to make the legged locomotion
environment training work. It includes the following:
* `ActionManager` class: To handle various action terms and provide
flexibility for HRL.
* Actuator simplification: We no longer have actuator groups. All that
is handled externally to the robot.
* Sensor optimization: Lazy sensor updates (only updated when `data` is
called)
* Update to new RSL-RL library
* TerrainImporter: It does import on initialization instead of expecting
input from users.

This MR breaks the behavior of the following (many of which need to be
fixed):
* `RobotBase` : Now there are two methods `write_commands_to_sim` and
`refresh_sim_data` that dictate sim read/write.
* `ActuatorGroups`: Doesn't exist anymore.
* `SensorBase`: Drop for the support of different backends (was not
supported earlier but now more explicit)

Fixes #37 , #36 

## Type of change

- Bug fix (non-breaking change which fixes an issue)
- New feature (non-breaking change which adds functionality)
- Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- This change requires a documentation update

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./orbit.sh --format`
- [ ] 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

---------
Co-authored-by: David Hoeller <dhoeller@ethz.ch>
Co-authored-by: Nikita Rudin <nrudin@nvidia.com>
Co-authored-by: Farbod Farshidian <ffarshidian@theaiinstitute.com>