TASK: Make it more obvious which value objects are persistent (part of the events)

[mhsdesign]

... also the persistent parts should probably reside in SharedModel or Common as discussed with @nezaniel #4961 (comment)

The thing im trying to address here is that one never knows if this dto is part of events and should better not be touched, and if so it has to be backwards compatible. I have no solution for that yet but ill keep this ticket as reminder.

For example when writing the unset migration, i noticed by accident that i would have to adjust the metadata.commandPayload.nodeTreeToInsert.childNodes[0].childNodes[0].propertyValues.myProperty which was really intransparent ^^
Also the fact the commands are serialised into the events metadata adds complexity as this could mean that a rebase / publish can become impossible if we change something.

[mhsdesign]

We should discuss when to use SharedModel vs Feature/Common