Add Doosan m1013 & m0609 manipulator

If you would like to see a new model added to the Menagerie collection, please provide us with the following information _before_ sending a pull request. (Ideally, before you start working on converting or tuning the model for MuJoCo.)

**URL for the existing model source (e.g. URDF)**
All the model files are in this dsr2 repo [descriptions](https://github.com/DoosanRobotics/doosan-robot2/tree/humble/dsr_description2).

**License terms of the upstream model**
BSD 3-Clause License: https://github.com/DoosanRobotics/doosan-robot2/blob/humble/LICENSE

**What do you think is required to convert and tune this model for MuJoCo?**
Currently changing this model for controlling robot in MuJoCo with ROS2! But might need little change for matching this repo request + MJX compatibility.

**Are you proposing to help develop and maintain the new model?**
I'm currenlty working at Doosan Robotics and sure! I'm willing to help. Should surely also contributes to Playground for next task!