SLA Email Enhancement

A validation has been added to ensure that the {ticket_number} placeholder is included in every SLA email body.
This guarantees that all SLA notifications contain the correct ticket reference for better clarity and tracking.

Key Updates:

• Required Placeholder
  Users must now include {ticket_number} in the SLA email body. Without it, the system will not allow saving or sending the email.

• Improved Accuracy
  Ensures all SLA notifications include the correct ticket reference, reducing confusion and improving communication consistency.

• Better User Guidance
  The validation clearly reminds users to add the placeholder, making SLA email setup more reliable and easier to manage.