Add warning for 'Auto Switch To Remote Scene Tree' setting

[Error7Studios]

Bugsquad edit: Depends on #1339.

Describe the project you are working on:
Card game (but applies to any project)

Describe the problem or limitation you are having in your project:
I noticed intermittent lag while testing my game, so I checked the profiler and saw huge lag spikes every second.
After Googling, I found a few relevent mentions of this issue:

• https://godotengine.org/qa/22467/lag-spikes-every-1s-using-c%23-in-3-0rc1
• https://www.reddit.com/r/godot/comments/bs4erz/psa_lagstutter_every_second_in_large_scene_trees/
• The Remote Scene Tree causes jerky movement everytime it updates godot#13219

The lag was being caused by the Remote SceneTree being updated, because I had enabled 'Auto Switch To Remote Scene Tree' in the Editor settings.

If I hadn't found those search results, it would have taken me a long time to discover the source of the lag.

Describe the feature / enhancement and how it helps to overcome the problem or limitation:
I think there should be a warning generated when you run your project with 'Auto Switch To Remote Scene Tree' enabled, explaining that this can cause lag spikes every second.

This should also be mentioned in the tooltip when you hover over this setting in the Editor Settings window.

Describe how your proposal will work, with code, pseudocode, mockups, and/or diagrams:

If this enhancement will not be used often, can it be worked around with a few lines of script?:
No.

Is there a reason why this should be core and not an add-on in the asset library?:
With no warning about the potential lag caused by having 'Auto Switch To Remote Scene Tree' enabled, this could make a lot of people think that they have an optimization problem when they don't.

[KoBeWi]

Printing a warning every time is rather meh (especially when the option is disabled by default).

The tooltip would be enough probably, but right now it can't be added, see godotengine/godot#29694