Set default FPS to 5 in kinect_rgbd.launch

[NFiedler]

Fixes #221

This fixes issue #221 by adapting the default FPS of the kinect_rgbd.launch file from 30 to 5 similar to the driver.launch file, as then, both files follow the documentation

Description of the changes:

• change the default value of the FPS parameter in the kinect_rgbd.launch file from 30 to 5

Required before submitting a Pull Request:

• [x] I reviewed CONTRIBUTING.md
• [ ] I built my changes locally
• [ ] I tested my changes with a device
• [ ] I changed both the ROS1 and ROS2 branches

I tested changes on:

• [ ] Windows
• [ ] Linux
• [ ] ROS1
• [ ] ROS2