Feature Request: Hooks and/or Environment Variables to override Settings

Hi there,

first of all, love the plugin, love the service. It simply works.

As we automate a lot of things in our CI-Pipelines it would be awesome if you could provide filters or ideally environment-variables/constants that we could use to overwrite the plugin-settings e.g. when deploying to staging.

This way we could react on the staging-environment and set API-Keys, Markting/Transactional, From-Settings, and Mime-Type in the wp-config.php using something like:

define('EE_MIME_TYPE', 'texthtml');
define('EE_EMAIL_TYPE', 'transactional');
// .... all the others

That would be soooo nice!

Thanks in advance!
David