Add iiwa_controller_v2: Implement hardware interface for KUKA iiwa7 via FRI

- Introduced iiwa_hardware_interface_plugin.xml to define the hardware interface.
- Created command_guard.hpp to enforce joint limits for position and torque commands.
- Developed fri_client.hpp and fri_client.cpp to manage FRI communication and state snapshots.
- Implemented system_interface.hpp and system_interface.cpp for lifecycle management and command handling.
- Added system_interface_type_values.hpp for extended state interface names.
- Defined package.xml for ROS2 integration with necessary dependencies.

src/iiwa_controller_v2/external

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