[ET-1563] Tickets Emails > Add Setting Tab Behind Constant

[codingmusician]

🎫 Ticket

ET-1563 ET-1545

🗒️ Description

This PR adds a constant that can be used to display the new Tickets Emails settings tab. You can use one of the following lines to get the tab to display.

// using a constant
define( 'TEC_TICKETS_EMAILS', true );

// or using a filter
add_filter( 'tec_tickets_emails_is_enabled', '__return_true' );

🎥 Artifacts

✔️ Checklist

• [ ] I've included a changelog entry in the readme.txt file.
• [x] My code is tested.
• [x] My code has proper inline documentation.