* feat: update the email addresses in the site config
* chore: update the default email address everywhere
* feat: update the template for the config
* chore: remove default_site_mail as an allowed parameter
* feat: change biz@dev.to to teh business email address and with a subject
* feat: update partners@dev.to to use SiteConfig.email_addresses[:business]
* feta: update to business email address
* feat: update members@dev.to to use the site config
* feat: update privacy email
* chore: Anna's suggestion to loop through object instead of keys
* Move from env variables to SiteConfig
Related to #5384
This PR only deals with the first remaining part outlined in the issue, starting to use existing SiteConfig keys instead of the env variables.
* Restore Envfile to original version for now
* Add registration view to sign_in page
* Add better sad path for failed sign ins/ups
* Ensure email is downcased for authorization
* Remove .downcase for emails
* Use partial for styles
