Add $PAYEE_FIRST_NAME$ as a field for invoice email template

The automatic email to tenants of new rental invoices currently only has the tenants full name (first name + surname) as an option in the email template.

Always looks very odd i.e. Hello Robert Jones, please find...

Can you add a first name option a bit like you have with $TENANT_FIRST_NAME$ in the mail merge templates?

Thank you!