Updated the paramater declaration in `publisher_forward_position_controller` to resolve a deprecation warning.

Changes Made:
- Replaced `self.declare_parameter(name)` with `self.declare_parameter(name, descriptor=ParameterDescriptor(dynamic_typing=True))`

Fixes: ros-controls#1239

Updated the paramater declaration to include type in `publisher_forward_position_controller` and `publisher_joint_trajectory_controller`

Changes Made:
- Replaced `self.declare_parameter(name)` with `self.declare_parameter(name, rclpy.Parameter.Type.DOUBLE_ARRAY)`