gh stack submit: Add options to config.yml to allow enabling --auto and/or --open by default

[bhamiltoncx]

Coming from Graphite gt submit, I expected gh stack submit to just do what I said: submit a prepared PR stack with appropriate titles and without opening an interactive UI.

There is gh stack submit --auto --open, but ~/.config/gh/config.yml doesn't seem to support specifying CLI options by default.

I can create an alias with gh stack alias, but that's hard to remember for something new.

Please add an option to config.yml to allow enabling --auto and/or --open to gh stack submit by default.