Quickly disable copilot and save its status in the project settings

I tried copilot from qtcreator master branch and it works great, congrats to all involved.

It's missing one little (well not that little) thing.

Using copilot is a bit controversial and some customers doesn't allow using it.

That's the reason why every single IDE that is using it, allows to users quickly disable it.

It will be great if qtcreator will add the same feature.
Besides that feature, it will be more useful if:

• the user can choose if copilot will be disabled by default or not when creating/opening a new project (this option should be in the Edit->Preference->Copilot page).
• save the copilot status in the project settings.