QLR import without replacing layer UUIDs

[gotjoshua]

Feature description

in QgsLayerDefinition::loadLayerDefinition the UUID is being replaced automatically, even if no conflict exists:

// IDs of layers should be changed otherwise we may have more then one layer with the same id
// We have to replace the IDs before we load them because it's too late once they are

I am coding up a plugin that adds deterministic export and git based sync for layer groups.
I want to be able to replace an existing layer group without replacing all the UUIDs.

Additional context

In my import process, i delete the existing layer group first, so the identical layers will not be a problem. If there was an optional flag to skipIDchange it will allow the changes to the layers to remain deterministic and accurately based on changes that actually happened.
As this would be an opt-in parameter it would not change existing functionality and is a very low hanging fruit to wrap the ID replacement in an if statement. (If it was typescript, this would be a PR, but i've yet to ever compile QGIS or any c++ project for that matter)