A warning is needed for turning off "Update Navigation Automatically", large nav meshes can cause crashes

A warning is needed before allowing users to uncheck update Navigation Automatically. A user has done so and then created a nav mesh that was 1,000,000 by 1,000,000 in size and they can no longer open their project due to the initial load.

1. Open the editor
2. Open the Editor settings
3. Uncheck Update Navigation Automatically
   Level Editor > Miscellaneous > Update Navigation Automatically
4. In the Level editor create a new Nav Mesh Bounds Volume
5. Notice you can set the scale to an extremely large number such as 1,000,000

Expected: A warning would be given either when scaling the nav mesh or when unchecking the update automatically option
Result: the project hangs when trying to save or potentially when trying to open

Limit navmesh creation 'work size' so it doesn't crash the editor