The default MultiplayerAPI is actually a SceneMultiplayer

**Your Godot version:**
v4.2.2.stable.official [15073afe3]

**Issue description:**
In the "High-level multiplayer" overview (Arguably the first link someone stumbles upon when googling "Godot multiplayer") it is said that by default, the multiplayer node already has a `MultiplayerAPI` configured. However, it's actually a [`SceneMultiplayer`](https://docs.godotengine.org/en/stable/classes/class_scenemultiplayer.html), that *inherits* MultiplayerAPI.
This is actually really important however, because you need to set `allow_object_decoding` in the `SceneMultiplayer` to true to send objects over the network, something which probably every Godot multiplayer game does. Each time I made a new multiplayer project I always stumbled over [this issue](https://github.com/godotengine/godot/issues/82718) and only then remembered that.
Considering how essential that option is, maybe it should also be mentioned in the "high-level multiplayer" overview.

**URL to the documentation page:**
https://docs.godotengine.org/en/stable/tutorials/networking/high_level_multiplayer.html#initializing-the-network