Add Zoom step

[fdebbabi]

First of all, thank you for your amazing terminal 👍

I want to be able to customize the zoom step using the configuration file.
I believe this is really useful when using big monitors so that I don't click a lot of zoom in/zoom out keymaps 😤

{
module.exports = {
    config: {
        fontSize: 12,
        fontFamily: 'Fira Code, Menlo, "DejaVu Sans Mono", Consolas, "Lucida Console", monospace',
        zoomStep: 2   // <---- Here is an example of the change
    },
    keymaps: {
       "zoom:in": "ctrl+i",
       "zoom:out": "ctrl+o",
    },
};