Explain some caveats in change tracking

[vmikhailenko]

Change tracking documentation is extended to attempt to clear two things that cause confusion between stakeholders:

• the element-defined identifier should not be used for compositions as it does very little sense for them.
• the stakeholders need to ensure that change-tracked entities are updated using deep updates from the root of the document (entity with compositions). Notably, the changes are not linked to their expected parents and this causes confusion.