Add option to pass additional parameters to the template

It would be nice to have an option to add a method that wraps the data passed to the page-renderer, providing the req. Something to the effect of:

const errorDataHandler = (data, req) => {
    data.body = req.body
    data.redirectTo = req.host
}
 await httpErrorPages.express(this.app, {
            errorDataHandler,
            lang: 'en_US',
            footer: `hello <strong>world</strong>`,
        })

I can include changes to express.js to demonstrate how I think this could work and provide that in a PR to be examined alongside this issue.

[AndiDittrich]

the req and ctx variables can be exposed to the filter callback of v3

[KenEucker]

@AndiDittrich Awesome, thank you so much, v3 is great! 🎉 👏 🎉