More documentation on the new multiplayer system

### Describe the project you are working on

A 2D multiplayer game

### Describe the problem or limitation you are having in your project

The documentation, in form of [this tutorial](https://godotengine.org/article/multiplayer-in-godot-4-0-scene-replication/#selecting-levels), and the [node docs](https://docs.godotengine.org/en/stable/classes/class_multiplayerspawner.html) lacks many details.

### Describe the feature / enhancement and how it helps to overcome the problem or limitation

I would like the documentation to answer the questions like:

1. when spawning new nodes and synchronizing parameters, what is the order of events? Ie. when are the parameters synced in respect to calling _ready, _enter_tree, etc.
2. How does changing the multiplayer authority affects MultiplayerSpawner/Synchronizer?
3. How do custom spawn works? Should one call `spawn` on all of the peers, or only on the server?
4. What happens when a spawn exceeds the spawn limit? Is the spawn unsuccessful, is error raised, or is one of the current nodes removed (which one)?
5. Which of the parameters can be synced?

I know you're working hard on making the docs better, I mostly wanted to pinpoint the topics that were not clear for me after reading the current docs.

### Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

More details in the same node docs that we have now.

### If this enhancement will not be used often, can it be worked around with a few lines of script?

Basic functionality.

### Is there a reason why this should be core and not an add-on in the asset library?

Basic functionality.