pqPresetGroupsManager: Combine User Setting and Default presets
Old Behavior:
If User settings exist, read TransferFunctionPresets.Groups from there, else read it from pqPresetGroups.json.
New Behavior:
If User settings exist, read TransferFunctionPresets.Groups from pqPresetGroups.json, and add the User group and the default presets not present in pqPresetGroups.json from User settings' TransferFunctionPresets.Groups
This is done to resolve #22657 (closed).
Backport: release
Edited by Spiros Tsalikis