Developers could use different protocol/host/port in development.

For instance, I use `https://gdk.test:3443`.
I noticed that links in emails point to `http://localhost:3000`.

This change should make links to be generated based on a developer's configs.

This setting is set by
`Rails.application.routes.default_url_options = default_url_options`
in `config/initializers/default_url_options.rb`.