Add MiR100 mobile robot

[aquintan4]

Adds the MiR100 as a new robot in RoboticsInfrastructure, ready for any exercise to use.

• New package under CustomRobots/mir100 with the robot description, sensor plugins and launch file, same structure as the other custom robots (turtlebot3, dingo).
• Real world dimensions and sensor placement ported from the mir_description package in mukmalone/mir_robot (DFKI GmbH, BSD 3-Clause). Credit and full license text kept in CustomRobots/mir100/LICENSE and NOTICE.
• Differential drive through gz-sim-diff-drive-system, the same mechanism turtlebot3 uses.
• Two SICK S300 lidars, front and back, matching the real sensor range and field of view.
• IMU using gz-sim-imu-system, same plugin used across the other robots.
• Odometry noise variants (low, medium, high) following the existing pattern used by turtlebot3 and dingo.
• Four new rows in the robots table in worlds.sql, base robot plus the three noise levels.