[Event Settings] Add mailer for changes to important settings #11938
Description
See parent issue for full context.
Add mailer for:
- When transparency mode is turned on. It should explain the feature and also suggest turning on monthly announcements
- When monthly announcements are turned on. It should explain the feature
The reason why we want to send these mailer when turning on features is because it only takes on manager to turn on the feature, and all managers may get emails about cancelled announcements, etc. We want to make sure all users are educated about the features.