set multipart mode (chunked is not supported)

[bmegli]

Currently we are auto selecting multipart if device supports multiple components

At the same time:

• we don't support chunked mode (no implementation)
• some devices will send data as chunks even for single component
  • if not explicitly asked for multipart

See:

• https://github.com/Extend-Robotics/camera_aravis/issues/21#issuecomment-1673200950
• where I needed hack in code to pull single component only as multipart (coming as chunk by default)

[bmegli]

For above reason it is better to let the user choose chunked/multipart mode (e.g. ROS argument)

[bmegli]

Or even just hardcode multipart (vs chunked) because this is the mode currently supported.