User Editor: "Update Expire Date" button
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A new button labeled "Update Expire Date" is added in the user
editor next to expire date field. This button can be used to
re-calculate the user's expire date based on the current profile's
permission interval and today's date.

This is similar to how the expire date is populated when creating a
new user, or when changing the profile group.

This button simplifies the process of "renewing" a user, by
eliminating the requirement that staff manually enter a new expire
date.

A button is used here so that the updating of the expire date
remains an  intentional process, not one that happens upon any edit.