FEATURE: 5054 - Add custom destination support for CreateNodeVariant

[nezaniel]

With this change, it is possible to select a destination parent / succeeding sibling for CreateNodeVariant, similar to CreateNodeAggregateWithNode and MoveNodeAggregate.

Upgrade instructions

none, all adjusted commands and events are downward compatible

Review instructions

none

Todo

• [x] constraint checks
• [ ] projection adjustments for handling the newish event
  • [ ] content graph
  • [ ] document uri path

[dlubitz]

You need to change the target branch to 9.1.