Improvements and generalisation of bag_publisher_maintain_time.cpp

[Ridhwanluthra]

The bag publisher with time maintainence is being added as a part of the perception_pipeline_tutorial.

This is node is used to read a topic from a bag and publish it on a loop while using the current ROS time. It is being added to use rosbags in tutorials which contain as less as a single message. This will enable us to add any bags corresponding to any tutorial right in git.

I would like to improve the working of this and generalise it to be usable by other tutorials as a utility.

[mlautman]

That would be great!