Missing support for changing MultiplayerSpawner authority is undocumented

**Your Godot version:**

4.4.1-stable

**Issue description:**

Currently, changing the authority of a `MultiplayerSpawner` does inevitably lead to errors and/or undocumented behavior including:

1. Nodes spawned prior to the authority transfer will not be despawned when the new authority deletes them.
2. If a new peer connects after an authority transfer prior to which objects were already spawned, the previous authority owner still tries to call `SceneReplicationInterface::_update_spawn_visibility` for the newly joined client, which of course causes an authorization error.

Looking at the relevant source code, I suspect that the spawner system was not really created with the possibility of `MultiplayerSpawner::set_multiplayer_authority` ever being called in mind, which is the reason I create this issue here instead of the main repository, as I am unsure if this would classify as a bug.

Unfortunately, though, neither the documentation nor the public API do communicate this intention to the user in any way, potentially leading to unexpected problems down the line.

I would propose to add a note to the respective documentation and preferably also add an error or warning message to `MultiplayerSpawner::set_multiplayer_authority` to immediately inform the user of this limitation.

**URL to the documentation page (if already existing):**

https://docs.godotengine.org/en/stable/classes/class_multiplayerspawner.html#multiplayerspawner