Feature description

Currently QgsLayerTreeViewIndicator is exposed in python but the provider is not.

This makes it very complicated to add an indicator with python.

All the indicators that are native to QGIS, as far as I can tell, use the provider rather than handling the indicator directly.

It's not only me who would find this useful:
https://gis.stackexchange.com/questions/417544/preserving-qgslayertreeviewindicator-on-moving-node-in-layer-tree-with-pyqgis

Additional context

No response