Upgrade launch file to use LaunchConfiguration/LaunchArguments for the port and baud rate.

Currently the two are hard-coded as node arguments and need to be manually edited in the launch file.

Tried replacing with LaunchArguments already by following a few examples found at the time, but could not get it to work. Limited help available on this issue, so leaving it open until it can be solved.

Branch [launch](https://github.com/ipa-kut/ros_marvelmind_package/tree/launch) has the trials.

Compare the launch branch with the current launch file, focusing on how the port and baud rate are passed as node arguments. First determine why the existing LaunchConfiguration/LaunchArguments trial did not work; done means both values can be supplied when launching without manually editing the file.

Written by the indexing model from the issue text.