Disable sending per environment

Problem/Motivation

Great module, btw, very useful. However, there is a pretty significant risk for sites that use separate development / testing / staging environments unless specific steps are taken.

If you have multiple environments with multiple copies of the database, there is a high probability of multiple abandoned cart emails (from each environment) being sent by accident, risking annoying and / or confusing customers. While this is true of any module that automatically sends emails, in my opinion, the risk is particularly high with this module.

Without some sort of notice, its an easy oversight to make, but an embarrassing one which has a relatively simple solution. I think users would appreciate the heads up.

Steps to reproduce

Create a couple of abandoned carts in production.
Prior to the next cron run, clone the database to a separate environment.
Trigger cron in both environments.

Proposed resolution

At a bare minimum, the module page / readme should highlight this risk and need for developers to take some action to prevent this behavior.

Better:
Once ✨ Option to disable email sending Active lands, suggest a config override (maybe link to https://www.drupal.org/docs/drupal-apis/configuration-api/configuration-... → ).

In the meantime, simply suggesting enabling test mode via config override would at least provide some positive way to prevent accidentally sending emails.

Remaining tasks

Update documentation / readme.