Add an option for creating staging certs for deployment testing

[wesharper]

Description
While working with infrastructure-as-code solutions like CDK, there's often a fair bit of trial and error with test deployments (at least for us). Often times, this amounts to the EC2 instance getting terminated with a new one taking its place. That means the setup runs from scratch each time.

A problem we encountered is that we got rate-limited for creating ssl certs using certbot for our custom domain on the staging deployment environment. It would be nice if we could pass a flag to use the certbot staging environment, which has much higher allotments. See (#77) for an example config.

Basic example
This could probably just be a simple env var or step in the user prompts during url setup that adds the --test-cert flag to the certbot command.

[brunoocasali]

Hi @wesharper thanks for the suggestion! Anybody is welcome to open a PR 🥇