Save "outline tab hidden" state, so that it can be disabled by default

[DanielDoesDesign]

Add a setting that hides the outline tab by default.

I dont use it enough to have it on the screen all the time. I can hide it, but then it comes back as it doesn't save the state of the setting.

[Maran23]

See also: #131
This is something that need to be implemented by Godot. And indeed, it is now (very recently). So that is fixed in Godot 4.6 (or the next dev version).