fix: malfunctioning launch script

[euyniy]

Issue

• openarm_bringup/openarm.launch.py was launching rviz2 with an incorrect configuration file.
• The same launch script is intended to execute xacro with a configurable prefix and support mock hardware. However, these features were not functioning as the required arguments and plugin initialization were missing from the xacro files.

Fix

• Updated the rviz configuration path to the correct file.
• Added the necessary arguments and plugin setup to the relevant xacro files to enable prefix configuration and mock hardware support.