Update ROS2 joint state menu graph to use state reader

[sylvesterkaczmarek]

Description

Update the Tools > Robotics > ROS 2 OmniGraphs > Joint States generator to use IsaacReadJointState as the source for ROS2PublishJointState.

ROS2PublishJointState now treats its direct targetPrim path as deprecated and recommends connecting IsaacReadJointState. The maintained MoveIt example already follows that path, while the menu generator still creates the legacy graph.

The generated publisher graph now:

• reads joint state with isaacsim.sensors.physics.IsaacReadJointState
• connects names, positions, velocities, efforts, DOF types, stage scale, and sensor time to ROS2PublishJointState
• triggers the publisher from the reader's execOut
• removes the redundant IsaacReadSimulationTime node from this graph

Subscriber/controller generation remains unchanged.

Validation

• updates the existing menu graph structure test to require IsaacReadJointState
• existing ROS 2 joint-state data-flow coverage remains in place
• modified Python files pass py_compile and git diff --check

Addresses the graph-template portion of #688 (internal ticket 6426353).