Option to call load_config service without triggering "There are unsaved changes" dialogue?

[FSund]

Calling the load_service service nearly always triggers a "There are unsaved changes" dialogue.

An option (perhaps via an additional field in the service definition) to always discard changes would be nice for our workflow.

[FSund]

I've had a look at the code, and it seems like this shouldn't require too many changes. Looks like a if (!discard_changes) around this prepareToExit() call should do the trick:
https://github.com/ros-visualization/rviz/blob/noetic-devel/src/rviz/visualization_frame.cpp#L750

This would mean adding a discard_changes argument to VisualizationFrame::loadDisplayConfigHelper.

I thought about adding a discard_changes field to SendFilePath.srv, but that seems like it should rather be a new service. Perhaps something like LoadConfig.srv

std_msgs/String path # absolute path to file or directory
bool discard_changes # discard changes to RViz config
---
bool success

The main issue is how to implement this sercice. I'm guessing changing the service type of load_config is not an option, since it would be a breaking change?

I could always make a new service like load_config_discard_changes or similarly, but that might pollute the namespace too much?

Let me know if you have any suggestions, and I'll try to make a proper PR.