Support for $partial_due_date in custom invoice template.

What version of Invoice Ninja are you running? v5

What environment are you running?
Hosted

Have you searched existing issues/requests?
Yes

Screenshots
n/a

Additional context

When customising an invoice we have access to the partial payments amount due via $partial_due variable. However, there is no mention of the partial's due date.

See the docs: No mention of a partial due date. Only the $partial_due variable.