Fix TrajectoryExecutionManager rejecting unrecognized parameters

[PierceCoyle]

Description

The on_set_parameters_callback in TrajectoryExecutionManager::initialize() has an else block that rejects all parameters that it doesn't recognize. This crashes MoveItPy with use_sim_time = True, resulting in the error message:

terminate called after throwing an instance of 'rclcpp::exceptions::InvalidParameterValueException'
  what():  parameter 'qos_overrides./clock.subscription.durability' could not be set: 
Aborted (core dumped)

The else block itself seems to be an anti-pattern mentioned in the comments of rclcpp's node.hpp.

Tested on ROS2 Jazzy, Ubuntu 24.04.

Resolves #2940
Related #2220, ros2/rclcpp#1587

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers