Use gtkwave --saveonexit flag once the fix is propogated to apio

[zapta]

This issue is for adding the '--saveonexit' to the gtkwave command of 'apio sim', to remind the user to save the changes before exit.

Currently we don't use it because it's broken and saves the .gtkw file without asking the user. This issue is to add it once this fix gtkwave/gtkwave#411 propogates to the gtkwave version that apio uses.