[ROS2] Inconsistent parameter names for compressed transport

[bjsowa]

The compressed transport plugin declares different parameters depending on the namespace of the node. When the node does not have a namespace specified (i.e. it operates under the root namespaces) the parameters will look like this:

camera.image_raw.format
camera.image_raw.jpeg_quality                                                                         
camera.image_raw.png_level

When the node is put under a namespace, the plugin will add a dot character to the parameter names:

.camera.image_raw.format
.camera.image_raw.jpeg_quality                                                                         
.camera.image_raw.png_level

I could publish a fix for that but I need to know which way is the intended one.