Serializable i.e. low level commands

[bwaidelich]

Commands are meant to capture the intent of a user to change the state of the system.
But due to the fact that we re-apply commands during a rebase (in order to avoid inconsistencies in the content graph) some commands have a "serialized counter-part" that is (more) idempotent than the original command (e.g. when creating a node, the default values of the schema at the time of the command should be taken into account and not change between rebases).

Those lower-level commands are already marked @internal but they can still be send to ContentRepository::handle() – We should change that by making a clear distinction between actual commands and those internal (aka serialized) commands.

The affected commands are:

• CreateNodeAggregateWithNode => CreateNodeAggregateWithNodeAndSerializedProperties
• SetNodeProperties => SetSerializedNodeProperties
• SetNodeReferences => SetSerializedNodeReferences

and potentially some more to come. e.g. today we discussed that CopyNodesRecursively should have a serialized counter-part too in order to better capture the intent (and to avoid that this command can be used to circumvent constraint checks)

Related: #5054

[bwaidelich]

Note: Those internal commands could be used to for faster processing, e.g. within importers / migrators. But IMO we should go for the separation (and with it for consistent behavior and extension points). If performance is the bottleneck, low-level services could always directly persist events

[bwaidelich]

Note: This can be closed once CopyNodesRecursively is removed from the core

[mhsdesign]

Copy Nodes is now only a low level command anymore, not public api: #5371 and will be removed