Move in product emails fully under ee as that is their only use

What does this MR do and why?

• move module
• add more test coverage
• re-organize some helper code as well
• resolve some rubocop exceptions and remove deleted files

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #427204 (closed)