Make the force push confirmation button configurable

**Is your feature request related to a problem? Please describe.**
Force pushing is a destructive operation. Currently the `enter` is used to confirm it. I've force pushed with lazygit on accident before, when I was going too fast or was clumsy.

**Describe the solution you'd like**
The consequences of mistakenly force pushing (e.g. if the user did not carefully read the dialog) could be dire, while the consequences of cancelling are mild, therefore it would be nice if we could configure the confirmation button to something unusual to our liking, e.g. the `f` key.

**Describe alternatives you've considered**
An easier to implement option would be simply changing the hardcoded `enter` button to another hardcoded button, but that would be backward incompatible and could upset some people.

**Additional context**
Converted from [discussions](https://github.com/jesseduffield/lazygit/discussions/1905#discussioncomment-2979181).