Feat: customize diffOutputPath detail

Hey guys, thanks for the great work of `cypress-image-snapshot`.

I have a little improvement(if it is) to suggest, blew is my case:
I've developed a NodeJS service based on Cypress and cypress-image-snapshot. In my project, I provided a platform to show reports details including diff images which cypress-image-snapshot produced of course. So I need to customized the reports content like:

```
See diff for details: https://XXX.XXX.com/diff_image.png
```

but not a hard coded abs path:

```
See diff for details: /XXX/XXX/diff_image.png
```

So I need a `resolveDiffOutputPath` function to customize the command details.

Waiting for your feedback, thanks in advance!